188 



PRINCIPLES OF ANIMAL BIOLOGY 



rounding air that the development of the eggs can scarcely be affected 

 by the presence of the parent. Some other species apparently incubate 

 the eggs to a small extent. The python, for example, coils about its 



Fig. 157. iio. i5<s. 



Fig. 157. — Hyla fuhrmanni Peracca, a South American tree frog that has the habit of 

 carrying the eggs on the back. The female carries the eggs. (Photograph by A. G. 

 Ruthven.) 



Fig. 158. — A marsupial frog, Gastrotheca monticola Barbour and Noble, from Peru. 

 The opening of the pouch and a protruding egg may be seen in the lumbar region. (Photo- 

 graph by G. K. Noble.) 



eggs, and as the temperature within its coils is a few degrees above that 

 of the surrounding atmosphere, development is thereby probably some- 

 what accelerated. 



The habit of carrying the eggs attached to the body is found in several 



groups, among both nest-building forms and 

 others that build no nests. Thus, the female 

 crayfish carries her eggs attached to the swim- 

 inerets under her abdomen, where she waves 

 them back and forth. The movement of the 

 eggs increases aeration, which is perhaps neces- 

 sary. Fresh-water mussels keep their eggs in 

 the chambers of the gills of the female, where 

 they are furnished oxygen by the water that is 

 constantly passing through the gills. In spiders 

 the silken egg case mentioned earlier is often 

 carried about by the mother. Certain frogs 

 (Fig. 157) and insects bear the eggs glued to the 

 back of one sex or the other. In other frogs 

 the eggs are attached to the belly, or the egg 

 masses are wrajiped around the hind legs of the 

 male or are held in the vocal sacs. One frog, the 

 marsupial frog (Fig. 158), has a pouch formed of a fold of the skin on the 

 back in which the eggs are carried. This habit is again found in the pipe- 

 fish and sea horse (Fig. 159) which carry the eggs in a ventral pouch.^ 



Fig. 159. — Hippo- 

 campus, the sea horse, 

 male specimen showing 

 brood pouch: hr. ap, 

 branchial aperture; brd. 

 p, brood poucli; df, dorsal 

 fin; op, opening of brood 

 pouch; pet. f. pectoral fin. 



