20 A BOOK OF INSECTS 



early stage of development. The young are turned out 

 in an unfinished state, so to speak, and are left to shift 

 for themselves. Starfishes, oysters, crabs, and many other 

 marine creatures start life in this way. The struggle for 

 existence is more fiercely contested in the sea than upon 

 the land ; infant mortality is rife ; and as an offset to this 

 ocean dwellers produce multitudinous young of which 

 only a few are destined to survive. Clearly a crab, which 

 lays many thousands of eggs, cannot provision each of 

 these with yolk as liberally as an animal which lays, 

 perhaps, only ten or a dozen eggs. Thus young crabs 

 hatch prematurely. They issue from the egg in a form 

 very unlike that of their parents, and pass through an 

 elaborate metamorphosis ere they reach the adult state. 



Naturalists were at one time inclined to regard the 

 larva of an insect simply as a prematurely hatched embryo 

 approximating to the young form of a crab or an oyster. 

 But more perfect knowledge has led them to adopt a 

 different view of the case. It is now known that the 

 eggs of insects, in common with those of almost all land 

 animals, are plentifully provisioned with yolk, so that the 

 need for premature hatching does not obtain. Moreover, 

 we have already seen that metamorphosis is complete only 

 among the more highly specialised forms of insect life, 

 while among primitive insects, like the cockroach, it is 

 slight. These facts suggest that metamorphosis among 

 insects is not a mere offset to infant mortality, but that 

 it is the outcome of successful conquest and established 

 supremacy. In other words, the transformations through 

 which a young insect passes cannot be regarded merely 

 as phases in its development, but as elaborate adaptations 

 to its changing conditions of life. 



Plow can complete metamorphosis among insects be 

 explained ? It is probably due in large measure to the 



