THE HAUNTS OF LIFE 121 



many birds that nest on the ground, the young, known 

 as Praecoces, are able to run about within a short period 

 after hatching ; and every one knows how quickly a 

 lamb or a foal gets on to its legs. 



In this connexion it is very interesting to notice that in 

 Amphibians which represent the transition-class between 

 aquatic and terrestrial life, there are not a few exceptions 

 in which the larval period, normally passed through in the 

 water, tends to be abbreviated by some peculiar device. 

 Thus the eggs of the South American Nototrema ovifera 

 are pushed by the male, after they are laid, into a pocket 

 on the female's back ; those of the Chilian Rhinoderma 

 are carried by the male in his resonating sacs ; those 

 of the Surinam Toad develop in a multitude of little skin- 

 pits on the female's back. 



(4) The fourth adaptation is one that might not naturally 

 occur to the non-zoological student. A thorough-going 

 terrestrial animal usually shows internal fertilization of the 

 eggs. In many fishes the eggs are deposited in the water 

 and the fertilizing fluid or milt is deposited upon them or 

 near them. But this is incompatible with the conditions 

 of terrestrial life. There are exceptional cases, it Is true, 

 but they tend to prove the rule. Thus one earthworm 

 fertilizes another, but the sperms are extruded again 

 in packets which project as tiny tags on the skin ; these 

 spermatophores are included in a barrel of mucus that 

 slips over the earthworm's head and forms the cocoon when 

 the eggs are liberated. What is laid in the ground is a 

 cocoon containing several eggs and numerous sperms. 



The terrestrial area has to be divided up into more sub- 

 divisions than any other haunt of life : it is so extraordinarily 

 diverse. We think, for instance, of mountains and islands, 



