EVIDENCE FROM EMBRYOLOGY 69 



these larval organs . . . are never properly func- 

 tional, since no actually free-swimming larva is 

 developed, but the embryo merely floats in the al- 

 buminous fluid of the cocoon. 



"A particularly beautiful example is offered by 

 the whales in their embryological development, which 

 has been thoroughly studied by Kiikenthal. In the 

 adult condition they show only the anterior ex- 

 tremities, but in the embryo the posterior pair, with 

 their skeletal parts, are formed, but are afterwards 

 completely atrophied. Although they are mammals, 

 in the adult condition they have absolutely no 

 covering of hair, since in their aquatic life another 

 and more effective protection against loss of heat is 

 given by means of a thick layer of blubber; only a 

 few coarse bristles, partly with particular functions, 

 have persisted on a few parts of the body. But in 

 the embryo a dense covering of hair is formed, which 

 is later transformed in a peculiar manner and 

 atrophied. Further, a series of whales have no 

 teeth in the adult condition, but only the well- 

 known, eel-trap like, horny plates, from which whale- 

 bone is produced. Nevertheless, in the embryo there 

 is a dentition of numerous teeth, which are, however, 

 resorbed, without ever piercing the gum." l 



Throughout the great group of the ruminants, 

 which includes the oxen, buffaloes, bison, sheep, 

 goats, antelopes, deer and giraffes, the collar-bone is 

 invariably lacking, since it is superfluous on account 



1 Otto Maas, in Die Abstammungslehre, pp. 273-4. 



