210 THE INFANCY OF ANIMALS 



has taken place earlier than in the young dog-fish, where- 

 in the external gills are absorbed before emergence from 

 the egg. One cannot suppress a feeling of surprise at 

 this most extraordinary exposure of the young, anchored 

 for weeks by the enormous weight of the provender they 

 must consume before they can contrive to move. It 

 seems impossible that so hampered they could avoid 

 the hosts of predatory animals by which they must be 

 surrounded : and that the shelter of the egg-shell would 

 be absolutely essential till this gargantuan feast had 

 been completed. 



This matter of the food yolk has here been brought 

 prominently to the front because of its bearing on what 

 has gone before and what is to follow, for no other animals 

 afford quite so striking a demonstration, perhaps, as to 

 the part played by this important source of nourishing 

 animals before they are able to feed themselves. We 

 may now turn with the more profit to the consideration 

 of the care which the eggs and young receive among 

 fishes. 



Commonly, as among the Amphibia, the eggs are small, 

 and are extruded, often in enormous numbers, to form 

 masses of " spawn." The shark tribe afford an inter- 

 esting exception to this rule, since they lay but. few, very 

 large eggs, and these are encased within a horny shell 

 which takes diverse shapes. In the dog-fish, for instance, 

 the egg-case is oblong and furnished at each corner with 

 a long tendril, which serves as an anchor. As the egg is 

 being extruded the fish swim round and round some 

 piece of upright seaweed, and the curling tendrils become 

 entwined therewith after the fashion shown in our illus- 

 tration. The egg-case of the Port Jackson Shark {Cestra- 

 cion) is pear-shaped, and surrounded by a broad spiral 



