NATURAL SCIENCES OF PHILADELPHIA. 279 



oppress my conviction that strong resemblances between human cranial types 

 do not infallibly indicate a common parentage, such resemblances merely 

 manifesting similarity of positional the human series.* Human osteology, 

 however, is not peculiar in this respect. Prof. Agassiz thinks that the circum- 

 stances under which were found the fossil remains obtained by Prof. Holmes 

 from the post-pliocene or post-tertiary beds of South Carolina, " show beyond 

 the possibility of a controversy," I am using his own strong language, 

 "that animals which cannot be distinguished from one another, may originate 

 independently in different fauna. "f It will thus be seen that in many in- 

 stances to refer a skull to its appropriate formal type is one thing ; to 

 refer it to its proper race, quite another. An obscure system of homoioke- 

 phalic representation seems to prevail among the races of men, in virtue of 

 which the cranial type of one race repeats itself among another people, very 

 distant from, and unknown to the first. Hence the law of cranial correlations 

 is, to a certain extent, obscured, and its utility in identifying and classifying 

 human skulls very much impaired. But the great difficulty after all with the 

 craniographer is to fix upon characters which are at once definitive, differen- 

 tial and constant, and therefore typical beyond all doubt or cavil. The skulls 

 of the orthognathic Greek, and the prognathic Saharan Negro differ more from 

 each other than do those of the nandu and ostrich, those of the llama and 

 eamel, or those of the genera Tarandus, Alces, Cervus, Panolia, Axis, Caria- 

 cas, Blastocerus, Capreolus and Cervulus into which naturalists divide the 

 Oervidse. But the negro differs cranially as much from the Eskimo, the Phoe- 

 nician and the Malay as from the Greek. Yet the Eskimo, the Phoenician 

 and the Malay, like the woolly-haired typical African, are all prognathic. The 

 prognathism of the one, however, differs in kind from that of each of the 

 others. Here, then, are differences which, though minute, serve to alter the 

 entire physiognomical expression of a skull, and so affect not only its classifi- 

 cation but its identity also. When we compare together extreme crania, 

 without reference to intervening forms,, these differences are seen to be differ- 

 ences of kind. But as soon as we take into' comparison the transitionary 

 cranial forms or types, which fill up the space or gap between these extremes, 

 then these differences become differences of degree rather than of kind. 



The same uncertainty characterises the species of many genera of birds, 

 reptiles, shells, plants, &c. Dr. Adam Smith placed in a row all the known 

 species of the natural family of the Alcaudae, and in presence of such an ordeal, 

 all the pretended specific external characters of naturalists completely broke 

 down. Dr. Knox dissected the serpents of South Africa, and divided them, 

 according to the dentition, into those with poison fangs, and those without. 

 This he regarded as a scientific distinction. But when he began to dissect the 

 serpents of the globe and not those of any particular region he quickly found , 

 that the distinction was invalid. That certain species of insects carry poisonous 

 fangs only on the upper maxillary bones is true ; but as there are many 

 which carry also harmless teeth on the same bones, the fact becomes of 

 little or no value scientifically or practically, t It is needless to multiply proof 

 in this direction. Indeed it seems to be a general fact that just in proportion 

 as the species of a genus become more and more numerous, their differential 

 characters become more and more confused and uncertain, and the species 

 when ranged side by side are seen to blend with or pass into each other in 

 obedience to a great, fundamental law of gradation through which their true 

 structural unity finds its only expression. Viewing the facts of specific differ- 

 ences in this comprehensive way, and bearing in mind that the question of 



* Crania' Characteristics of the Races of Men, in Indigenous Races of the Earth, p. 

 349. 



t See his letter to Prof. Holmes in Proc. Acad Nat. Sci. loc. citat., p. 186. 



t Contributions to the Philosophy of Zoology, with special references to the Natural 

 History of Man. London Lancet, November, 1855, p. 386. 



1859.] 



