The Variation of Animals and Plants under Domestication — Volume 1

(FIGURE 24. SKULLS OF PIGEONS viewed laterally, of natural size. A. Wild Rock-pigeon, Columba livia. B. Short-faced Tumbler. C. English Carrier. D. Bagadotten Carrier.)

[SKULL.

The individual bones, especially those at the base, do not differ in shape. But the whole skull, in its proportions, outline, and relative direction of the bones, differs greatly in some of the breeds, as may be seen by comparing the figures of (A) the wild rock-pigeon, (B) the Short-faced Tumbler, (C) the English Carrier, and (D) the Bagadotten Carrier (of Neumeister), all drawn of the natural size and viewed laterally. In the Carrier, besides the elongation of the bones of the face, the space between the orbits is proportionally a little narrower than in the rock-pigeon. In the Bagadotten the upper mandible is remarkably arched, and the premaxillary bones are proportionally broader. In the Short-faced Tumbler the skull is more globular: all the bones of the face are much shortened, and the front of the skull and descending nasal bones are almost perpendicular: the maxillo-jugal arch and premaxillary bones form an almost straight line; the space between the prominent edges of the eye-orbits is depressed. In the Barb the premaxillary bones are much shortened, and their anterior portion is thicker than in the rock-pigeon, as is the lower part of the nasal bone. In two Nuns the ascending branches of the premaxillaries, near their tips, were somewhat attenuated, and in these birds, as well as in some others, for instance in the Spot, the occipital crest over the foramen was considerably more prominent than in the rock- pigeon.

(FIGURE 25. LOWER JAWS, seen from above, of natural size. A. Rock-pigeon. B. Runt. C. Barb.

FIGURE 26. SKULL OF RUNT, seen from above, of natural size, showing the reflexed margin of the distal portion of the lower jaw.

FIGURE 27. LATERAL VIEW OF JAWS, of natural size. A. Rock-pigeon. B. Shortfaced Tumbler. C. Bagadotten Carrier.)

In the lower jaw, the articular surface is proportionably smaller in many breeds than in the rock-pigeon; and the vertical diameter, more especially of the outer part of the articular surface, is considerably shorter. May not this be accounted for by the lessened use of the jaws, owing to nutritious food having been given during a long period to all highly improved pigeons? In Runts, Carriers, and Barbs (and in a lesser degree in several breeds), the whole side of the jaw near the articular end is bent inwards in a highly remarkable manner; and the superior margin of the ramus, beyond the middle, is reflexed in an equally remarkable manner, as may be seen in figure 25, in comparison with the jaw of the rock-pigeon. This reflection of the upper margin of the lower jaw is plainly connected with the singularly wide gape of the mouth, as has been described in Runts, Carriers, and Barbs. The reflection is well shown in figure 26 of the head of a Runt seen from above; here a wide open space may be observed on each side, between the edges of the lower jaw and of the premaxillary bones. In the rock-pigeon, and in several domestic breeds, the edges of the lower jaw on each side come close up to the premaxillary bones, so that no open space is left. The degree of downward curvature of the distal half of the lower jaw also differs to an extraordinary degree in some breeds, as may be seen in the drawings (figure 27 A) of the rock-pigeon, (B) of the Short-faced Tumbler, and (C) of the Bagadotten Carrier of Neumeister. In some Runts the symphysis of the lower jaw is remarkably solid. No one would readily have believed that jaws differing in the several above-specified points so greatly could have belonged to the same species.

VERTEBRAE.

All the breeds have twelve cervical vertebrae. (5/36. I am not sure that I have designated the different kinds of vertebra correctly: but I observe that different anatomists follow in this respect different rules, and, as I use the same terms in the comparison of all the skeletons, this, I hope, will not signify.) But in a Bussorah Carrier from India the twelfth vertebra carried a small rib, a quarter of an inch in length, with a perfect double articulation.

The DORSAL VERTEBRAE are always eight. In the rock-pigeon all eight bear ribs; the eighth rib being very thin, and the seventh having no process. In Pouters all the ribs are extremely broad, eight bear ribs; the eighth rib being very thin and the seventh having no process. In Pouters all the ribs are extremely broad, and, in three out of four skeletons examined by me, the eighth rib was twice or even thrice as broad as in the rock-pigeon; and the seventh pair had distinct processes. In many breeds there are only seven ribs, as in seven out of eight skeletons of various Tumblers, and in several skeletons of Fantails, Turbits and Nuns.

In all these breeds the seventh pair was very small, and was destitute of processes, in which respect it differed from the same rib in the rock- pigeon. In one Tumbler, and in the Bussorah Carrier, even the sixth pair had no process. The hypapophysis of the second dorsal vertebra varies much in development; being sometimes (as in several, but not all Tumblers) nearly as prominent as that of the third dorsal vertebra; and the two hypapophyses together tend to form an ossified arch. The development of the arch, formed by the hypapophyses of the third and fourth dorsal vertebrae, also varies considerably, as does the size of the hypapophysis of the fifth vertebra.

The rock-pigeon has twelve sacral vertebrae; but these vary in number, relative size, and distinctness, in the different breeds. In Pouters, with their elongated bodies, there are thirteen or even fourteen, and, as we shall immediately see, an additional number of caudal vertebrae. In Runts and Carriers there is generally the proper number, namely twelve; but in one Runt, and in the Bussorah Carrier, there were only eleven. In Tumblers there are either eleven, or twelve, or thirteen sacral vertebrae.

The CAUDAL VERTEBRAE are seven in number in the rock-pigeon. In Fantails, which have their tails so largely developed, there are eight or nine, and apparently in one case ten, and they are a little longer than in the rock- pigeon, and their shape varies considerably. Pouters, also, have eight or nine caudal vertebrae. I have seen eight in a Nun and Jacobin. Tumblers, though such small birds, always have the normal number seven; as have Carriers, with one exception, in which there were only six.

The following table will serve as a summary, and will show the most remarkable deviations in the number of the vertebra and ribs which I have observed: —

TABLE 4 . NUMBER OF VERTEBRAE AND RIBS IN:

1. THE ROCK PIGEON.

Cervical Vertebrae: 12.

Dorsal Vertebrae: 8.

Dorsal Ribs: 8.

The 6th pair with processes, the 7th pair without a process.

Sacral Vertebrae: 12.

Caudal Vertebrae: 7.

Total: 39.

2. POUTER, FROM MR. BULT.

Cervical Vertebrae: 12.

Dorsal Vertebrae: 8.

Dorsal Ribs: 8.

The 6th and 7th pair with processes.

Sacral Vertebrae: 14.

Caudal Vertebrae: 8 or 9.

Total: 42 or 43.

3. TUMBLER, DUTCH ROLLER.

Cervical Vertebrae: 12.

Dorsal Vertebrae: 8.

Dorsal Ribs: 7.

The 6th and 7th pair without processes.

Sacral Vertebrae: 11.

Caudal Vertebrae: 7.

Total: 38.

4. BUSSORAH CARRIER.

Cervical Vertebrae: 12.

The twelfth bore a small rib.

Dorsal Vertebrae: 8.

Dorsal Ribs: 7.

The 6th and 7th pair without processes.

Sacral Vertebrae: 11.

Caudal Vertebrae: 7.

Total: 38.

The PELVIS differs very little in any breed. The anterior margin of the ilium, however, is sometimes a little more equally rounded on both sides than in the rock-pigeon. The ischium is also frequently rather more elongated. The obturator-notch is sometimes, as in many Tumblers, less developed than in the rock-pigeon. The ridges on the ilium are very prominent in most Runts.

(FIGURE 28. SCAPULAE, of natural size. A. Rock-pigeon. B. Short-faced Tumbler.)

In the bones of the extremities I could detect no difference, except in their proportional lengths; for instance, the metatarsus in a Pouter was 1.65 inch, and in a Short-faced Tumbler only .95 in length; and this is a greater difference than would naturally follow from their differently-sized bodies; but long legs in the Pouter, and small feet in the Tumbler, are selected points. In some Pouters the SCAPULA is rather straighter, and in some Tumblers it is straighter, with the apex less elongated, than in the rock-pigeon: in figure 28, the scapula of the rock-pigeon (A), and of a short-faced Tumbler (B), are given. The processes at the summit of the CORACOID, which receive the extremities of the furculum, form a more perfect cavity in some Tumblers than in the rock-pigeon: in Pouters these processes are larger and differently shaped, and the exterior angle of the extremity of the coracoid, which is articulated to the sternum, is squarer.

(FIGURE 29. FURCULA, of natural size. A. Short-faced Tumbler. B and C Fantail. D. Pouter.)

The two arms of the FURCULUM in Pouters diverge less, proportionally to their length, than in the rock-pigeon; and the symphysis is more solid and pointed. In Fantails the degree of divergence of the two arms varies in a remarkable manner. In figure 29, B and C represent the furcula of two Fantails; and it will be seen that the divergence in B is rather less even than in the furculum of the short-faced, small-sized Tumbler (A), whereas the divergence in C equals that in a rock-pigeon, or in the Pouter (D), though the latter is a much larger bird. The extremities of the furculum, where articulated to the coracoids, vary considerably in outline.

In the STERNUM the differences in form are slight, except in the size and outline of the perforations, which, both in the larger and lesser sized breeds, are sometimes small. These perforations, also, are sometimes either nearly circular, or elongated as is often the case with Carriers. The posterior perforations occasionally are not complete, being left open posteriorly. The marginal apophyses forming the anterior perforations vary greatly in development. The degree of convexity of the posterior part of the sternum differs much, being sometimes almost perfectly flat. The manubrium is rather more prominent in some individuals than in others, and the pore immediately under it varies greatly in size.]

CORRELATION OF GROWTH.

By this term I mean that the whole organisation is so connected, that when one part varies, other parts vary; but which of two correlated variations ought to be looked at as the cause and which as the effect, or whether both result from some common cause, we can seldom or never tell. The point of interest for us is that, when fanciers, by the continued selection of slight variations, have largely modified one part, they often unintentionally produce other modifications. For instance, the beak is readily acted on by selection, and, with its increased or diminished length, the tongue increases or diminishes, but not in due proportion; for, in a Barb and Short-faced Tumbler, both of which have very short beaks, the tongue, taking the rock-pigeon as the standard of comparison, was proportionally not shortened enough, whilst in two Carriers and in a Runt the tongue, proportionally with the beak, was not lengthened enough, thus, in a first-rate English Carrier, in which the beak from the tip to the feathered base was exactly thrice as long as in a first-rate Short-faced Tumbler, the tongue was only a little more than twice as long. But the tongue varies in length independently of the beak: thus in a Carrier with a beak 1.2 inch in length, the tongue was .67 in length: whilst in a Runt which equalled the Carrier in length of body and in stretch of wings from tip to tip, the beak was .92 whilst the tongue was .73 of an inch in length, so that the tongue was actually longer than in the carrier with its long beak. The tongue of the Runt was also very broad at the root. Of two Runts, one had its beak longer by .23 of an inch, whilst its tongue was shorter by .14 than in the other.

With the increased or diminished length of the beak the length of the slit forming the external orifice of the nostrils varies, but not in due proportion, for, taking the rock-pigeon as the standard, the orifice in a Short-faced Tumbler was not shortened in due proportion with its very short beak. On the other hand (and this could not have been anticipated), the orifice in three English Carriers, in the Bagadotten Carrier, and in a Runt (pigeon cygne), was longer by above the tenth of an inch than would follow from the length of the beak proportionally with that of the rock-pigeon. In one Carrier the orifice of the nostrils was thrice as long as in the rock- pigeon, though in body and length of beak this bird was not nearly double the size of the rock-pigeon. This greatly increased length of the orifice of the nostrils seems to stand partly in correlation with the enlargement of the wattled skin on the upper mandible and over the nostrils; and this is a character which is selected by fanciers. So again, the broad, naked, and wattled skin round the eyes of Carriers and Barbs is a selected character; and in obvious correlation with this, the eyelids, measured longitudinally, are proportionally more than double the length of those of the rock-pigeon.

The great difference (see figure 27) in the curvature of the lower jaw in the rock-pigeon, the Tumbler, and Bagadotten Carrier, stands in obvious relation to the curvature of the upper jaw, and more especially to the angle formed by the maxillo-jugal arch with the premaxillary bones. But in Carriers, Runts, and Barbs the singular reflexion of the upper margin of the middle part of the lower jaw (see figure 25) is not strictly correlated with the width or divergence (as may be clearly seen in figure 26) of the premaxillary bones, but with the breadth of the horny and soft parts of the upper mandible, which are always overlapped by the edges of the lower mandible.

In Pouters, the elongation of the body is a selected character, and the ribs, as we have seen, have generally become very broad, with the seventh pair furnished with processes; the sacral and caudal vertebrae have been augmented in number; the sternum has likewise increased in length (but not in the depth of the crest) by .4 of an inch more than would follow from the greater bulk of the body in comparison with that of the rock-pigeon. In Fantails, the length and number of the caudal vertebrae have increased. Hence, during the gradual progress of variation and selection, the internal bony framework and the external shape of the body have been, to a certain extent, modified in a correlated manner.

Although the wings and tail often vary in length independently of each other, it is scarcely possible to doubt that they generally tend to become elongated or shortened in correlation. This is well seen in Jacobins, and still more plainly in Runts, some varieties of which have their wings and tail of great length, whilst others have both very short. With Jacobins, the remarkable length of the tail and wing-feathers is not a character which is intentionally selected by fanciers; but fanciers have been trying for centuries, at least since the year 1600, to increase the length of the reversed feathers on the neck, so that the hood may more completely enclose the head; and it may be suspected that the increased length of the wing and tail-feathers stand in correlation with the increased length of the neck- feathers. Short-faced Tumblers have short wings in nearly due proportion with the reduced size of their bodies; but it is remarkable, seeing that the number of the primary wing-feathers is a constant character in most birds, that these Tumblers generally have only nine instead of ten primaries. I have myself observed this in eight birds; and the Original Columbarian Society (5/37. J.M. Eaton 'Treatise' edition 1858 page 78.) reduced the standard for Bald-head Tumblers from ten to nine white flight- feathers, thinking it unfair that a bird which had only nine feathers should be disqualified for a prize because it had not ten WHITE flight- feathers. On the other hand, in Carriers and Runts, which have large bodies and long wings, eleven primary feathers have occasionally been observed.

Mr. Tegetmeier has informed me of a curious and inexplicable case of correlation, namely, that young pigeons of all breeds which when mature become white, yellow, silver (i.e., extremely pale blue), or dun-coloured, are born almost naked; whereas pigeons of other colours are born well- clothed with down. Mr. Esquilant, however, has observed that young dun Carriers are not so bare as young dun Barbs and Tumblers. Mr. Tegetmeier has seen two young birds in the same nest, produced from differently coloured parents, which differed greatly in the degree to which they were at first clothed with down.

I have observed another case of correlation which at first sight appears quite inexplicable, but on which, as we shall see in a future chapter, some light can be thrown by the law of homologous parts varying in the same manner. The case is, that, when the feet are much feathered, the roots of the feathers are connected by a web of skin, and apparently in correlation with this the two outer toes become connected for a considerable space by skin. I have observed this in very many specimens of Pouters, Trumpeters, Swallows, Roller-tumblers (likewise observed in this breed by Mr. Brent), and in a lesser degree in other feather-footed pigeons.

The feet of the smaller and larger breeds are of course much smaller or larger than those of the rock-pigeon; but the scutellae or scales covering the toes and tarsi have not only decreased or increased in size, but likewise in number. To give a single instance, I have counted eight scutellae on the hind toe of a Runt, and only five on that of a Short-faced Tumbler. With birds in a state of nature the number of the scutellae on the feet is usually a constant character. The length of the feet and the length of the beak apparently stand in correlation; but as disuse apparently has affected the size of the feet, this case may come under the following discussion.

ON THE EFFECTS OF DISUSE.

In the following discussion on the relative proportions of the feet, sternum, furculum, scapulae, and wings, I may premise, in order to give some confidence to the reader, that all my measurements were made in the same manner, and that they were made without the least intention of applying them to the following purpose.

[TABLE 5.I.

PIGEONS WITH THEIR BEAKS GENERALLY SHORTER THAN THAT OF THE ROCK-PIGEON, PROPORTIONALLY TO THE SIZE OF THEIR BODIES.

Column 1. Name of Breed.

Column 2. Actual length of Feet (inches).

Column 3. Difference between actual and calculated length of feet, in proportion to length of feet and size of body in the Rock-pigeon.

Column 3a. Too short by (inches).

Column 3b. Too long by (inches).

1. 2. 3a. 3b.

Wild rock-pigeon (mean measurement). 2.02

Short-faced Tumbler, bald-head. 1.57 0.11 ..

Short-faced Tumbler, almond. 1.60 0.16 ..

Tumbler, red magpie. 1.75 0.19 ..

Tumbler, red common (by standard to end of tail). 1.85 0.07 ..

Tumbler, common bald-head. 1.85 0.18 ..

Tumbler, roller. 1.80 0.06 ..

Turbit. 1.75 0.17 ..

Turbit. 1.80 0.01 ..

Turbit. 1.84 0.15 ..

Jacobin. 1.90 0.02 ..

Trumpeter, white. 2.02 0.06 ..

Trumpeter, mottled. 1.95 0.18 ..

Fantail (by standard to end of tail). 1.85 0.15 ..

Fantail (by standard to end of tail). 1.95 0.15 ..

Fantail crested var. Ditto. 1.95 0.0 0.0

Indian Frill-back Ditto. 1.8O 0.19 ..

English Frill-back. 2.10 0.03 ..

Nun. 1.82 0.02 ..

Laugher. 1.65 0.16 ..

Barb. 2.00 0.03 ..

Barb. 2.00 .. 0.03

Spot. 1.90 0.02 ..

Spot. 1.90 0.07 ..

Swallow, red. 1.85 0.18 ..

Swallow, blue. 2.00 .. 0.03

Pouter. 2.42 .. 0.11

Pouter, German. 2.30 .. 0.09

Bussorah Carrier. 2.17 .. 0.09

Number of specimens. 28 22 5

I measured most of the birds which came into my possession, from the feathered BASE of the beak (the length of beak itself being so variable) to the end of the tail, and to the oil-gland, but unfortunately (except in a few cases) not to the root of the tail; I measured each bird from the extreme tip to tip of wing; and the length of the terminal folded part of the wing, from the extremity of the primaries to the joint of the radius. I measured the feet without the claws, from the end of the middle toe to the end of the hind toe; and the tarsus and middle toe together. I have taken in every case the mean measurement of two wild rock-pigeons from the Shetland Islands, as the standard of comparison. The following table shows the actual length of the feet in each bird; and the difference between the length which the feet ought to have had according to the size of body of each, in comparison with the size of body and length of feet of the rock- pigeon, calculated (with a few specified exceptions) by the standard of the length of the body from the base of the beak to the oil-gland. I have preferred this standard, owing to the variability of the length of tail. But I have made similar calculations, taking as the standard the length from tip to tip of wing, and likewise in most cases from the base of the beak to the end of the tail; and the result has always been closely similar. To give an example: the first bird in the table, being a Short- faced Tumbler, is much smaller than the rock-pigeon, and would naturally have shorter feet; but it is found on calculation to have feet too short by .11 of an inch, in comparison with the feet of the rock-pigeon, relatively to the size of the body in these two birds, as measured from the base of beak to the oil-gland. So again, when this same Tumbler and the rock-pigeon were compared by the length of their wings, or by the extreme length of their bodies, the feet of the Tumbler were likewise found to be too short in very nearly the same proportion. I am well aware that the measurements pretend to greater accuracy than is possible, but it was less trouble to write down the actual measurements given by the compasses in each case than an approximation.

TABLE 5.II.

PIGEONS WITH THEIR BEAKS LONGER THAN THAT OF THE ROCK-PIGEON, PROPORTIONALLY TO THE SIZE OF THEIR BODIES.

Column 1. Name of Breed.

Column 2. Actual length of Feet (inches).

Column 3. Difference between actual and calculated length of feet, in proportion to length of feet and size of body in the Rock-pigeon.

Column 3a. Too short by (inches).

Column 3b. Too long by (inches).

1. 2. 3a. 3b.

Wild rock-pigeon (mean measurement). 2.02

Carrier. 2.60 .. 0.31

Carrier. 2.60 .. 0.25

Carrier. 2.40 .. 0.21

Carrier, Dragon. 2.25 .. 0.06

Bagadotten Carrier. 2.80 .. 0.56

Scanderoon, white. 2.80 .. 0.37

Scanderoon, Pigeon cygne. 2.85 .. 0.29

Runt. 2.75 .. 0.27

Number of specimens. 8 .. 8

In these two tables (Tables 5.I.and 5.II.) we see in the first column the actual length of the feet in thirty-six birds belonging to various breeds, and in the two other columns we see by how much the feet are too short or too long, according to the size of bird, in comparison with the rock- pigeon. In the first table twenty-two specimens have their feet too short, on an average by a little above the tenth of an inch (viz.107); and five specimens have their feet on an average a very little too long, namely, by .07 of an inch. But some of these latter cases can be explained; for instance, with Pouters the legs and feet are selected for length, and thus any natural tendency to a diminution in the length of the feet will have been counteracted. In the Swallow and Barb, when the calculation was made on any standard of comparison besides the one used (viz. length of body from base of beak to oil-gland), the feet were found to be too small.

In the second table we have eight birds, with their beaks much longer than in the rock-pigeon, both actually and proportionally with the size of body, and their feet are in an equally marked manner longer, namely, in proportion, on an average by .29 of an inch. I should here state that in Table 5.I. there are a few partial exceptions to the beak being proportionally shorter than in the rock-pigeon: thus the beak of the English Frill-back is just perceptibly longer, and that of the Bussorah Carrier of the same length or slightly longer, than in the rock-pigeon. The beaks of Spots, Swallows, and Laughers are only a very little shorter, or of the same proportional length, but slenderer. Nevertheless, these two tables, taken conjointly, indicate pretty plainly some kind of correlation between the length of the beak and the size of the feet. Breeders of cattle and horses believe that there is an analogous connection between the length of the limbs and head; they assert that a race-horse with the head of a dray-horse, or a grey-hound with the head of a bulldog, would be a monstrous production. As fancy pigeons are generally kept in small aviaries, and are abundantly supplied with food, they must walk about much less than the wild rock-pigeon; and it may be admitted as highly probable that the reduction in the size of the feet in the twenty-two birds in the first table has been caused by disuse (5/38. In an analogous, but converse, manner, certain natural groups of the Columbidae, from being more terrestrial in their habits than other allied groups, have larger feet. See Prince Bonaparte 'Coup d'oeil sur l'Ordre des Pigeons.'), and that this reduction has acted by correlation on the beaks of the great majority of the birds in Table 5.I. When, on the other hand, the beak has been much elongated by the continued selection of successive slight increments of length, the feet by correlation have likewise become much elongated in comparison with those of the wild rock-pigeon, notwithstanding their lessened use.

As I had taken measures from the end of the middle toe to the heel of the tarsus in the rock-pigeon and in the above thirty-six birds, I have made calculations analogous with those above given, and the result is the same — namely, that in the short-beaked breeds, with equally few exceptions as in the former case, the middle toe conjointly with the tarsus has decreased in length; whereas in the long-beaked breeds it has increased in length, though not quite so uniformly as in the former case, for the leg, in some varieties of the Runt varies much in length.

LENGTH OF STERNUM.

As fancy pigeons are generally confined in aviaries of moderate size, and as even when not confined they do not search for their own food, they must during many generations have used their wings incomparably less than the wild rock-pigeon. Hence it seemed to me probable that all the parts of the skeleton subservient to flight would be found to be reduced in size. With respect to the sternum, I have carefully measured its extreme length in twelve birds of different breeds, and in two wild rock-pigeons from the Shetland Islands. For the proportional comparison I have tried three standards of measurement, with all twelve birds namely, the length from the base of the beak to the oil-gland, to the end of the tail, and from the extreme tip to tip of wings. The result has been in each case nearly the same, the sternum being invariably found to be shorter than in the wild rock-pigeon. I will give only a single table, as calculated by the standard from the base of the beak to the oil-gland; for the result in this case is nearly the mean between the results obtained by the two other standards.

TABLE 5.III.

LENGTH OF STERNUM.

Column 1. Name of Breed.

Column 2. Actual Length in Inches.

Column 3. Too short by (inches).

1. 2. 3.

Wild Rock-pigeon. 2.55

Pied Scanderoon. 2.80 0.60

Bagadotten Carrier. 2.80 0.17

Dragon. 2.45 0.41

Carrier. 2.75 0.35

Short-faced Tumbler. 2.05 0.28

Barb. 2.35 0.34

Nun. 2.27 0.15

German Pouter. 2.36 0.54

Jacobin. 2.33 0.22

English Frill-back. 2.40 0.43

Swallow. 2.45 0.17

This table (Table 5.III.) shows that in these twelve breeds the sternum is of an average one-third of an inch (exactly .332) shorter than in the rock- pigeon, proportionally with the size of their bodies; so that the sternum has been reduced by between one-seventh and one-eighth of its entire length; and this is a considerable reduction.

I have also measured in twenty-one birds, including the above dozen, the prominence of the crest of the sternum relatively to its length, independently of the size of the body. In two of the twenty-one birds the crest was prominent in the same relative degree as in the rock-pigeon; in seven it was more prominent; but in five out of these seven, namely, in a Fantail, two Scanderoons, and two English Carriers, this greater prominence may to a certain extent be explained, as a prominent breast is admired and selected by fanciers; in the remaining twelve birds the prominence was less. Hence it follows that the crest exhibits a slight, though uncertain, tendency to be reduced in prominence in a greater degree than does the length of the sternum relatively to the size of body, in comparison with the rock-pigeon.