The Development of the Alligator 229 



In most — probably all normal — eggs a white 

 band appears around the lesser circumference a 

 short time after being laid. This chalky band, 

 which is shown at about its maximum development 

 in Fig. la, is found, on removal of the shell, to be 

 caused, not by a change in the shell, but by the 

 appearance of an area of chalky substance in the 

 shell membranes. Clarke thinks this change in 

 the membrane is to aid in the passage of gases to 

 and from the developing embryo. Generally this 

 chalky area forms a distinct band entirely around 

 the shorter circumference of the egg, but sometimes 

 extends only partly around it. It varies in width 

 from about 15 mm. to 35 mm., being narrowest at 

 its first appearance. Sometimes its borders are 

 quite sharp and even (Fig. la); in other cases they 

 are very irregular. If the embryo dies the chalky 

 band is likely to become spotted with dark areas. 



The shell and shell membrane of the egg of the 

 Madagascar crocodile are essentially the same as 

 those just described, except that the shell is some- 

 times pierced by small pores that pass entirely 

 through it. The same chalky band surrounds the 

 median zone of the egg (78). 



The white of the egg is chiefly remarkable for its 

 unusual density, being so stiff that the entire egg 

 may be emptied from the shell into the hand and 

 passed from one hand to the other without danger 

 of rupturing either the mass of albumen or the 

 enclosed yolk. The albumen, especially in the 



