Ohap. XIV.] DEVELOPMENT AlfD EMBRYOLOGY. 241 



cannot be given than the statement by Von Baer that* 

 the embryos of mammalia, of birds, lizards, and 

 snakes, probably also of chelonia are in their earliest 

 " states exceedingly like one another, both as a whole 

 and in the mode of development of their parts; so 

 "much so, in fact, that we can often distinguish the 

 embryos only by their size. In my possession are two 

 " little embryos in spirit, whose names I have omitted 

 to attach, and at present I am quite unable to say to 

 " what class they belong. They may be lizards or small 

 ''' birds, or very young mammalia, so complete is 

 •' the similarity in the mode of formation of the head 

 "and trunk in these animals. The extremities, how- 

 " ever, are still absent in these embryos. But even 

 "if they had existed in the earliest stage of their de- 

 "velopment we should learn nothing, for the feet of 

 "lizards and mammals, the wings and feet of birds, 

 " no less than the hands and feet of man, all arise from 

 "the same fundamental form." The larvas of most 

 crustaceans, at corresponding stages of development, 

 closely resemble each other, however different the adults 

 may become; and so it is with very many other ani- 

 mals. A trace of the law of embryonic resemblance 

 occasionally lasts till a rather late age: thus birds of 

 the same genus, and of allied genera, often resemble 

 each other in their immature plumage; as we see in the 

 spotted feathers in the young of the thrush group. In 

 the eat tribe, most of the species when adult are striped 

 or spotted in lines; and stripes or spots can be plainly 

 distinguished in the whelp of the lion and the puma. 

 We occasionally though rarely see something of the 

 same kind in plants; thus the first leaves of the ulex or 

 furze, and the first leaves of the phyllodineous acacias. 



