142 CHILDHOOD OF ANIMALS 



in Chili, the male has a pair of sacs, normally used to increase the 

 volume of the voice, which open into the mouth on each side of 

 the tongue. In the breeding season the fertilised eggs, which are 

 only from five to fifteen in number, are placed in this, and as the 

 embryos develop, the sacs expand until they occupy the whole of 

 the lower surface of the body under the skin. Not only hatching 

 takes place in this secure retreat, but also the further development 

 of the young, which do not emerge until they are miniatures of the 

 adult. In Rhacophorus reticulatus, a Ceylonese tree-frog, there are 

 only about twenty eggs produced, and these after being laid are 

 attached to the under surface of the skin of the female, where they 

 are carried about in little pits, until the tadpoles hatch out. In the 

 Surinam toad, the male spreads the eggs, which are also few in 

 number, on the back of the female, where each sinks into a little 

 cup-shaped depression, afterwards covered by a lid, and are thus 

 carried about until the metamorphosis is completed. In Hyla 

 goeldii, a South American tree-frog, there are between twenty and 

 thirty large eggs, which are carried on the back of the mother, 

 supported by a flap or fold of the skin ; and in the tree-frogs of the 

 genus Nototrema, which also live in South America, the females 

 have a well-developed pouch of the skin, placed on the back and 

 opening backwards, in which the eggs are carried until they are 

 either tadpoles or young frogs. 



In all reptiles the number of the family has been greatly re- 

 duced, and not more than from six or seven to about one hundred 

 are produced at a time, except in some of the turtles and tortoises. 

 The eggs are large, containing enough food-yolk to nourish the 

 embryo until it is hatched in a condition closely resembling that 

 of the parent, except in size and pattern, but large and strong enough 

 to look after itself. In consequence of this, the old larval stages are 

 suppressed, and although the embryo passes through a phase when 

 it has gill slits and the appearance of an aquatic creature, this 

 takes place before hatching, and the young are terrestrial. Even 

 the aquatic reptiles come on land to breed, and there are no 

 more than vague reminiscences of their gill-breathing ancestors. 

 The eggs are enclosed in a firm shell, sometimes tough and leathery, 

 sometimes hard and brittle, but nearly always white in colour. In 

 most cases, the eggs are hatched outside the body, but in a few 

 snakes and lizards they are retained until the young are born, in 

 these cases the shells being very thin. Brood-care is almost com- 

 pletely confined to a choice of the place in which the eggs are to be 



