iv.] METAMORPHOSES OF INSECTS. 65 



type of its section, from which the type of the class, 

 order, &c., is only afterwards developed." Agassiz 

 also observes that " the embryos of different animals 

 resemble each other the more the younger they are." 



There are, no doubt, cases in which the earlier 

 states are rapidly passed through, or but obscurely 

 indicated ; yet we may almost state it as a general 

 proposition, that either before or after birth animals 

 undergo metamorphoses. The state of develop- 

 ment of the young animal at birth varies immensely. 

 The kangaroo (Macropus, major}, which attains 

 a height of seven feet ten inches, does not when 

 born exceed one inch and two lines in length ; 

 the chick leaves the egg in a much more advanced 

 condition than the thrush ; and so, among insects, 

 the young cricket is much more highly developed, 

 when it leaves the egg, than the larva of the fly 

 or of the bee ; and, as I have already mentioned, 

 differences occur even within the limit of one species, 

 though not of course to anything like the same 

 extent. 



In oviparous animals the condition of the young 

 at birth depends much on the size of the egg : where 

 the egg is large, the abundant supply of nourish- 

 ment enables the embryo to attain a high stage of 

 development ; where the egg is small, arid the yolk 

 consequently scanty, the embryo requires an addi- 

 tional supply of food before it can do so. In the 

 former case the embryo is more likely to survive ; but 

 when the eggs are large, they cannot be numerous, 

 and a multiplicity of germs may be therefore in some 

 circumstances a great advantage. Even in the same 



I F 



