VARIETIES OF MANKIND. 



1307 





increases with great regularity, constituting 

 the Madrepora verrucosa of Fabricius. If it 

 cluster round the cylindrical and branching 

 stem of a Fucus, it increases irregularly, and 

 assumes the form of the Millcpora tubulosa of 

 Ellis. If its development in any direction be 

 checked by a mechanical obstacle, the form of 

 the mass will again be changed, and its tubes 

 will be recurved backwards; a character on 

 which Lamouroux founded his genus Obcita. 

 Sometimes on the very same polypidom, we 

 find one portion whose disposition corre- 

 sponds with that of Millepora tubulosa, and 

 another which, if detached, would be con- 

 sidered a specimen of Obclia tubulifcra.* 

 Many similar cases might be quoted ; all of 

 them showing, not that there is any real con- 

 fusion amongst species and genera, but that 

 naturalists have too often assumed variable 

 and non-essential characters as the basis of 

 their systematic distinctions, in ignorance of 

 those which are fixed and determinate. Thus, 

 in the case in question, it is on the structure 

 of the animal, not on the form of the poly- 

 pidom, that the modern Zoophytologist places 

 his chief reliance ; and a knowledge of this 

 would have prevented the assignment of the 

 varieties of coral, formed by one and the same 

 kind of animal, to three different genera. So 

 among Mollusca, it has been shown by Mr. 

 Gray -J- that a large number of species have been 

 formed, in consequence of the variations pre- 

 sented by the shells of the same species at 

 different periods of life, or developed under 

 different circumstances. The change from 

 salt or fresh water to brackish, or from 

 brackish to salt or fresh, which many species 

 are able to sustain, appears to have a con- 

 siderable influence on the form of their shells ; 

 thus Professor E. Forbes has shown that 

 certain Paludin<E and Naticce, which are found 

 in successive tertiary strata in the island of 

 Cos, associated in some cases with decidedly 

 fresh-water, and in others with decidedly 

 marine, testacea, are probably to be regarded 

 as varieties of the same species, notwith- 

 standing that they would be regarded by 

 conchologists as distinct ; gradations being 

 traceable between one form and another, 

 and the changes being of a kind which are 

 known to take place among fresh-water mol- 

 lusca. J 



As an example of the mode in which the 

 philosophic zoologist proceeds in his exami- 

 nation of a doubtful case of unity or diversity 

 of species, in a group more closely related to 

 man, we shall consider the question of the 

 relations of the several races of Dogs to each 

 other. Every one is familiar with the fact 

 that numerous breeds of dogs exist in 

 almost every part of the world inhabited by 

 civilised man, distinguished from each other 

 by well-marked peculiarities, which appear 

 to be transmitted continuously from parent 



* Memoire sur les Tubulipores, in Ann. des Sci. 

 Nat., 2eme seVie, Zool. torn. viii. 



t On the Structure of the Shells of Mollusca, 

 Philosophical Transactions, 1833. 

 Travels in Lycia, vol. ii. p. 199. 



to offspring, and thus to possess a claim 

 to rank as specific distinctions. These dif- 

 ferences extend to stature, form, proportions, 

 swiftness of foot, colour and texture of hair, 

 acuteness of sensations, intelligence, and at- 

 tachment to man ; and they are particularly 

 well marked in the conformation of the cra- 

 nium, the part to which the anatomist first 

 looks for his distinctive characters. 

 i. The changes in the conformation of the 

 cranial portion of the skull, which distinguish 

 the domesticated races of the dog from those 

 which have been less modified by the r in- 

 fluence of man, partly consist in the obli- 

 teration of the sagittal crest, which rises 

 up on the line of junction of the parietal 

 bones, and of its continuation on the occipital 

 bone. In the large deer-hound, we are 

 assured by Prof. Owen, these cristae are as 

 strongly developed as in the wolf; whilst in 

 the smaller spaniel or pug, they are entirely 

 wanting, the cranial dome being smooth and 

 round. But " such modifications," as Prof. 

 Owen remarks, " are unaccompanied by any 

 change in the connections, that is in the dis- 

 position of the sutures, of the cranial bones ; 

 they are chiefly due to arrests of develop- 

 ment, to retention of more or less of the 

 character of immaturity ; even the large pro- 

 portional size of the brain in the smaller va- 

 rieties of house-dog, is in a great degree due 

 to the rapid acquisition by the cerebral organ 

 of its specific size, agreeably with the general 

 law of its development, but which is attended 

 in the varieties cited by an arrest of the gene- 

 ral growth of its body, as well as of the par- 

 ticular developments of the skull in relation 

 to the muscles of the jaws." Such an altera- 

 tion is considered by this eminent anatomist 

 as fairly referable to the influence of domes- 

 tication ; since, as he remarks, " no other 

 domestic animal manifests so great a range of 

 variety in regard to general size, to the colour 

 and character of the hair, and to the form of 

 the head, as it is affected by different propor- 

 tions of cranium and face, and by the inter- 

 muscular crests superadded to the cranial 

 parietes." " Yet under the extremest mask of 

 variety so superinduced," he continues, " the 

 naturalist detects in the dental formula, and 

 in the construction of the cranium, the un- 

 mistakable generic and specific characters of 

 the Canis familiaris."" * Generally speaking, 

 the cranial cavity of the domesticated dogs is 

 relatively increased in capacity ; the facial por- 

 tion, on the other hand, is oftener shortened. 

 The skull of the Australian dingo differs but 

 little from that of a wolf. In both, the arch 

 formed by the temporal and parietal bones is 

 much depressed, so that the cranial cavity is 

 small, and the head flat. The Danish dog 

 and the mastiff resemble the dingo in the 

 shape of their heads, and display as little of 

 intellect or sagacity. The terrier and the 

 hound have the parietal bones more arched, 

 and, consequently, possess a larger cranial 

 cavity. The greyhound has a longer muzzle, 

 and smaller frontal sinuses than the hound ; 

 * Zoological Transactions, vol. iii. p. 415. 



