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 todry. 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. porosus, 
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- 
1 Voeltzkow, A., ‘The Biology and Development of the Outer Form 
of the Madagascar Crocodile,’ Abhandl. Senckberg. Gesell., Bd. 26, 
Hft, I, 
