70 POPULAR SCIENCE MONTHLY. 



the water; and the young remain within the egg until they are com- 

 plete frogs in shape. While passing through so much of their life- 

 history within the egg shell, the young manage to breathe, not by their 

 tails, but by special folds of skin that grow out on either side of the 

 belly, in rows, as shown in Fig. 1. The young frog also makes a tem- 

 porary contrivance for breaking through the egg shell, something like 

 the horn on the beak of a hatching chick or the protuberance used by 

 many reptiles for the same purpose. This peculiar little organ in the 

 frog is shown in Fig. 1 and again in Fig. 2, where it adds a decided 

 retrousse element to a not too intellectual countenance. 



"We might place frogs in three groups: those that are simply layers, 

 those that are nest-makers, and those that are nurses.* 



As a nest builder we may reckon the Cystignathus mystaceus of 

 Brazil. This frog makes a hole about as big as a teacup under stones 

 or decayed logs near enough to puddles of water to be covered by 

 water when the pond rises after heavy rains. In this nest the yellow 

 eggs are laid in a mass of thick, white foam, very like beaten white of 

 egg in appearance. The eggs hatch into tailed tadpoles, and, when the 

 water rises over the nest, these young swim off like our common tad- 

 poles. They differ, however, in being able to overtide dr}' seasons. 

 When the pond dries up and common tadpoles would die, these pecul- 

 iar creatures gather under boards or logs and there keep moist — 

 apparently by the aid of an imusual amount of material secreted by 

 their skins. Evidently the habits of this frog are nicely adjusted to 

 the climatic conditions under which it lives. 



A tree-frog of West Africa (Chiromantis rufescens) lays its eggs in 

 leaves of trees in a mass of foamy material that, on drying, hardens 

 on the outside, but becomes liquid within, and so lets the tadpoles swim 

 about for a while till a rain washes them off the tree into the water. 

 While living the short part of its tadpole stage in the nest made by the 

 mother for it, the tadpole has gills such as our common tadpoles 

 breathe with, as well as a tail to swim with. In this aerial existence 

 the young have the protection not only of the surrounding foam, but 

 often of leaves that are sometimes stuck to it. This perfecting of the 

 nest by the use of leaves to envelop the foam mass becomes the rule 

 in two sorts of frog in Brazil (Phyllomedusa Jheringii and Hyla neh- 

 ulosa). The former puts its big white eggs into a mass 40-50 mm. 

 long and 15-20 wide, enveloped by two or three leaves, sometimes 

 willow tree leaves, in such a way that they make a tight case open at 

 one end. The young seem to be so fitted for this peculiar wet-hara- 



* The remarkable life histories not in the first group have recently been brought 

 together by R. Wiedersheim, from whose papers in the 'Biologisches Central- 

 blatt' most of the facts and illustrations used in this article are taken. 



