ANIMAL PEDIGREES 223 



frog can only accomplish a small part of its de- 

 velopmental history within the egg, and must then 

 hatch in order to obtain food from without. Con- 

 sequently a frog hatches not as a frog but as a 

 tadpole i.e., at the fish stage in the ancestral 

 history of frogs. At the time of hatching there 

 are no limbs and no lungs ; the heart, the ali- 

 mentary canal, and the nervous system are in an 

 extremely imperfect condition ; while other organs 

 of the adult frog, such as the kidneys, have not yet 

 commenced to appear. The frog has therefore to 

 effect the greater part of its development after the 

 time of hatching. 



In the little West Indian frog, Hylodes, the 

 course of events is very different. This frog 

 which is of small size less than a couple of 

 inches in length lays its eggs not in water but on 

 the leaves of plants. The eggs are large, having 

 a diameter of about i inch i.e., are about three 

 times the diameter and twenty-seven times the 

 bulk of the eggs of the common English frog. The 

 large size of the egg is caused as we have seen 

 by great abundance of food yolk ; and the con- 

 sequence of this large supply of food yolk in the 

 egg of Hylodes is that the frog is enabled to 

 complete the whole of its development before 

 hatching, and emerges from the egg capsule in a 

 form differing from the adult merely in the posses- 

 sion of a rudimentary stump of a tail ; and even 

 this disappears before the close of the first day of 

 its existence. 



A further and direct consequence of this de- 



