The Biology of the Crocodilia 23 



vegetable matter of which the nest is composed. 

 Possibly heat may be derived from both of these 

 sources, but it seems likely that the conditions 

 that are especially favorable to normal incubation 

 are moisture and an even, though not necessarily 

 an elevated, temperature. Moisture is certainly 

 a necessary condition, as the porous shell allows 

 such rapid evaporation that the egg is soon killed 

 if allowed to dry. The inside of the nest is always 

 damp, no matter how dry the outside may become 

 under the scorching sun, so that this condition is 

 fully met. The eggs of the Madagascar crocodile, 

 according to Voeltzkow,^ offer a marked contrast 

 to those of the alligator. Instead of being laid 

 in damp nests of decaying vegetation, they are 

 laid in holes that are dug in the dry sand, and are 

 very sensitive to moisture, the early stages, espe- 

 cially, being soon killed by the least dampness. A 

 crocodile's nest containing eggs is shown in Figure 

 5. In this species of crocodile, probably C. porosiis, 

 the nest resembles that of the Florida alligator. 

 The photograph was taken by Mr. Rowley on the 

 edge of a small lake on the Island of Palawan, P. I. 

 The daily range of temperature in the Southern 

 swamps is sometimes remarkably great, so that if 

 the eggs were not protected in some way they would 

 often pass through a range of temperature of pos- 



' Voeltzkow, A., "The Biology and Development of the Outer Form 

 of the Madagascar Crocodile," Abhandl. Senckberg. Gesell., Bd. 26, 

 Hft. I. 



