180 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
freely in the sea. However, these larval organs... . are never 
properly functional, since no actually free-swimming larva is developed 
but the embryo merely floats in the albuminous fluid of the cocoon. 
“A particularly beautiful example is offered by the whales in their 
embryological development, which has been thoroughly studied by 
Kukenthal. In the adult condition they show only the anterior 
extremities, 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 embryoa 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.””* 
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 of 
the exclusively locomotive manner in which the fore legs are employed. 
In the embryo sheep the collar-bone is established and even, to some 
extent ossified, but is subsequently resorbed and disappears entirely. 
No doubt, the collar-bone will be found in many other embryo rumi- 
nants, when the proper examination shall have been made, but its 
demonstrated presence in the foetal sheep is sufficiently striking. In 
the higher mammals the number of teeth was originally 44, or 11 on 
each side of both upper and lower jaws, but in most of the modern or 
existing groups of these higher mammals this number has been very 
considerably reduced through the suppression: of certain teeth. We 
have every reason to believe that the ancestors of the forms with 
reduced dentition possessed teeth in full numbers and that there has 
actually been a loss of teeth in the course of descent. This conclusion 
is abundantly confirmed by the facts of embryology. Take, for 
example, the great group of the gnawing mammals or Rodentia, in 
which the front teeth or incisors, above and below, are reduced to one 
on each side, except in the rabbits. The incisors are chisel-shaped and 
* Otto Maas, Die Abstammungslehre, pp. 273-74. 
