Chap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 241 



better proof of this latter fact cannot be given than the 

 statement by Von Baer chat " 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 mam- 

 "malia, so complete is the similarity in the mode 

 " of formation of the head and trunk in these animals. 

 "The extremities, however, are still absent in these 

 " embryos. But even if they had existed in the earliest 

 " stage of their development 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 larvte 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 

 animals. 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 cat 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, 



