200 



PRINCIPLES OF ANIMAL BIOLOGY 



female, where they are furnished oxygen by the water that is constantly 

 passing through the gills. In spiders, the silken egg case mentioned 



Fig. 152. — ^Blue-tailed skink, Plestiodon fasciatus (Linnseus), -with eggs. This lizard 

 buries its eggs (the white mass in the middle foreground) in decaying wood and stays with 

 them until hatched. Probably the incubation of the eggs is not assisted by the presence of 

 the parent. The curved white streak to the left of the center of the picture is the tail 

 (blue in life) of the parent, and a part of the striped body can be seen to the right of the 

 center. (Photo by A. G. Ruthven.) 



Fig. 153. Fig. 154. 



Fig. 15.3. — Hyla fuhrmanni Peracca, a South American tree-frog which has the habit 

 of carrying the eggs on the back. The female carries the eggs, and the larval (tadpole) 

 stage is passed in the egg, the young emerging from the egg membrane in the adult stage. 

 (Photo by A. G. Ruthven.) 



Fig. 154. — A marsupial frog, Gastrotheca monticola Barbour and Noble, from Peru. 

 The female carries the eggs in a large poucli on the back. The opening of the pouch 

 and a protruding egg may be seen in the lumbar region. (Photo by G. K. Noble.) 



above is often carried about by the mother. Certain frogs (Fig. 153) and 

 insects bear the eggs glued to the back of one sex or th(^ other. In other 

 frogs the eggs are attached to the belly, or the egg masses arc wrapped 



