DOMESTIC LIFE. 137 



The egg-shell among the reptiles varies greatly 

 in its texture, being of great hardness in some 

 forms, as in some tortoises and in crocodiles for 

 example, and soft and leathery or parchment-like 

 in others, as in most lizards and in snakes. In 

 these cases, where the shell is of sufficient density 

 to require this, the snout of the embryo is pro- 

 vided with a sharp conical " tooth " wherewith 

 the shell is cut, just as among the birds. In 

 colour the shell is white or yellowish, but with- 

 out markings as in birds, save in the Tuatera 

 lizard, the egg-shell of which may bear a zone 

 of reddish spots. 



Eggs which have only a parchment-like shell, 

 be it noted, sometimes exhibit the strange feature 

 of growing after they have been laid. This 

 growth is due to the stretching of the shell by 

 the developing embryo, which in addition to 

 feeding on the contained food material, takes in 

 air and moisture through the shell. 



The number of the eggs varies, among the 

 tortoises, for example, some species laying from 

 three to five, others as many as one hundred 

 and twenty. Among the birds, it may be 

 remembered, there are many species, which lay 

 but a single egg, and more in which the number 

 does not exceed three. 



That the reptiles' eggs are invariably white 

 is to be explained by the fact that they are 

 never exposed, but laid either in holes of trees, 

 or burrows, or buried in the ground. 



With many reptiles great care is displayed in 

 the disposal of the eggs. Thus the European 

 Pond-tortoise first prepares the ground by water- 



