LIMITATION IN LOWER VERTEBRATES 145 



to think that this happens in most of the species. In any case the 

 newly hatched young remain together for a time, and tolerate each 

 other's presence. Healthy crocodiles and alligators, young or old, 

 are rather savage creatures, when the water in which they are kept 

 is not so cold that they are torpid. They are ready to snap at any 

 moving object, or even at a piece of wood thrown into their 

 pool. And yet, although there are occasional accidents, they are 

 gregarious, seldom attacking one another savagely unless in an 

 actual struggle for food. Individuals of all sizes and of several 

 kinds may be kept safely together. This instinct of toleration for 

 their own kind is, no doubt, the result of the association of the 

 young with each other and with the mother. The voice is certainly 

 used as a recognition call. The strong musky odour, due to a 

 secretion from glands at the root of the tail, but which pervades the 

 whole body, may possibly also serve for recognition, but I have 

 never been able to detect the odour in young animals. 



Lizards lay relatively large eggs, the numbers varying from two 

 to twenty or thirty. The process cf incubation takes a long time, 

 and when the young creatures emerge they are fully formed, 

 differing from their parents only in size and colour. They are 

 usually white, or very pale, and lie quietly for a few days, and then 

 set about the business of life without any assistance or guardian- 

 ship from their parents. Little trouble is taken even about the 

 deposition of the eggs. They are usually placed in holes on the 

 ground, in heaps of leaves, or in any natural cavities. A certain 

 number are viviparous that is to say, the eggs hatch just before 

 they are laid. The slow-worm, one of the common English lizards 

 (Lacerta vivipara), some of the chameleons and many of the skinks 

 are viviparous. Thus although brood -care among lizards is passive, 

 the large size of the eggs and still more the occasional viviparous 

 habit secure that the newly hatched or born creatures are mature 

 enough to be independent, and the number of the family has been 

 reduced. 



The eggs of snakes are large, usually very elongated and en- 

 closed in a soft, but tough, shell. They are not very numerous, 

 varying from three or four to fifty. They are fertilised before they 

 leave the body of the mother, but the length of time they are 

 retained seems to vary a good deal even in individuals of the same 

 species, with the result that some eggs when they are laid contain 

 only the merest microscopic trace of the embryo, whilst in others 

 the young snakes may be almost ready to hatch. Snakes, in fact, 

 C.A. K 



