DOMESTIC LIFE. 135 



as large since they do not come under the 

 influence of selection. 



The snakes, like the lizards, afford instances 

 of sexual differences in colour, but there seems 

 to be no evidence that these creatures fight for 

 their mates, and hence perhaps the absence of 

 all weapons save poison, and this is only associated 

 with the capture of food or the slaughter of 

 foes. 



On the whole, there is far less activity and 

 intensity of feeling displayed by the reptiles in 

 their choice of a mate than is the case with the 

 birds, as those who may have read the Story of 

 Bird-life will probably have remarked. 



Similarly, in the care they display for their 

 offspring, the reptiles are far behind the birds. 

 With the latter, it may be remarked, the young 

 are produced from eggs only after a long period 

 of incubation, but in many reptiles the eggs are 

 often retained within the body during the whole 

 process of their development, so that the young 

 are ready to leave the shell immediately after 

 the egg is deposited, or are even born free. 

 It is of importance to note that whilst in some 

 reptiles the internal development pf the egg is 

 normal, in others it occurs only when for some 

 reason laying is retarded. In this, probably, we 

 have the clue to the origin of the normal cases 

 of internal development. 



When the development of the egg takes place 

 outside the body, incubation by the mother rarely 

 takes place. Instead, the eggs are buried in warm 

 earth or decaying vegetable matter and there 

 hatch out. It is probable that in those rare 



