usually impossible to distinguish between the eggs of snakes, turtles and lizards 

 except by means of habitat, time of discovery and logical possibilities based on 

 distribution and abundance of local species. Some snakes lay in manure piles 

 or among rotting leaves where the heat of fermentation aids in incubation. 

 Others lay under logs or under thin, flat stones that absorb and retain heat 

 from the sun. Most egg-laying snakes produce ovoid eggs, although the eggs 

 of a few snakes are almost spherical. The alligator lays eggs about the size and 

 shape of goose eggs in piles of rotting vegetation in swamps. Most of the 

 lizards bury their eggs and pay them no further attention. Some species of 

 lizards deposit their eggs in rotting logs, damp moss or similar places and remain 

 with them to help incubate or protect them. The turtles bury their eggs in 

 warm, damp sand. The species of snapping turtles, mud and musk turtles, 

 and the soft'shells lay spherical eggs. The eggs of most of the other turtles 

 are ovoid. 



Birds' eggs have limy shells that crack easily. In general birds that nest 

 on the ground or in open nests have mottled or colored eggs, while those that 

 nest in dark cavities of hollow trees, caves or chimneys lay white or pale eggs. 

 Thus the bluebird, like other members of the thrush family, lays blue eggs, but 

 in conformity with its habit of nesting in holes in trees its eggs are only faintly 

 tinted with blue. Birds that build no nests but use a hollow on the ground or 

 a depression in a rock usually lay eggs pointed at one end and therefore having 

 less tendency to roll. Birds' eggs are most appealing from the aesthetic point 

 of view but are not readily available for collection because of strict laws re- 

 stricting the taking of eggs of most species. For purposes of study and identi' 

 fication, birds' eggs are very satisfactory because of definite specific sizes, color 

 and markings. Unlike the eggs of most of the other groups, a great deal of 

 information has been collected about the eggs of birds, and several good books 

 are available about them. 



GENERAL REFERENCES 

 Comstock, J. H. 1925. An Introduction to Entomology. (Second edition.) 



The Comstock Publishing Co. Ithaca. 

 Davie, O. 1900. Nests and Eggs of North American Birds. David McKay, 



Publisher. Philadelphia. 

 Dickerson, M. C. 1906. The Frog Book. Doubleday, Page and Co. New 



York. (Reprinted in 1933) 



Ditmars, R. L. 1936. The Reptiles of North America. Doubleday, Doran 

 and Co. New York. 



Gentry, T. G. 1882. Nests and Eggs of Birds of the United States. J. A. 



Wagenseller. Philadelphia. 

 Reed, C. A. 1904. North American Birds Eggs. Doubleday, Page and Co. 



New York. 

 Wright, A. H. 1932. Life Histories of the Frogs of Okefinokee Swamp, 



Georgia. The Macmillan Co. New York. 



542 



