HIS. SEDGWICK 



in 1859 that specific characteristics were often developed 

 precociously. " The Snapping Turtle, for instance, exhibits 

 its small crosslike sternum, its long tail, its ferocious habits, 

 even before it leaves the egg, before it breathes through 

 lungs, before its derm is ossified to form a bony shield, 

 etc. ; nay, it snaps with its gaping jaws at anything 

 brought near, when it is still surrounded by its amnion and 

 allantois, and its yolk still exceeds in bulk its whole body " 

 (p. 269). 



Wilhelm His, 1 in the course of an acute and damaging 

 criticism of the biogenetic law as enunciated by Haeckel, 

 showed clearly that by careful examination the very earliest 

 embryos of a whole series of Vertebrates could be dis- 

 tinguished with certainty from one another. " An identity 

 in external form of different animal embryos, despite the 

 common affirmation to the contrary, does not exist. Even 

 at early stages in their development embryos possess the 

 characters of their class and order, nay, we can hardly doubt, 

 of their species and sex, and even their individual character- 

 istics" (201). 



This specificity of embryos was affirmed with even greater 

 confidence by Sedgwick in a paper critical of von Baer's law. 2 

 He wrote : " If v. Baer's law has any meaning at all, surely 

 it must imply that animals so closely allied as the fowl and 

 duck would be indistinguishable in the early stages of develop- 

 ment ; and that in two species so closely similar that I 

 was long in doubt whether they were distinct species, viz., 

 Peripatus capensis and Balfouri, it would be useless to look 

 for embryonic differences ; yet I can distinguish a fowl and 

 a duck embryo on the second day by the inspection of a 

 single transverse section through the trunk, and it was the 

 embryonic differences between the Peripatuses which led 

 me to establish without hesitation the two separate species. . . . 

 I need only say . . . that a species is distinct and distinguish- 

 able from its allies from the very earliest stages all through 

 the deve-lopment, although these embryonic differences do 

 not necessarily implicate the same organs as do the adult 

 differences" (p. 39). 



1 Unsere Korperform, Leipzig, 1874. 

 - Q.J.M.S., xxxvi., pp. 35-52, 1894. 



