XII] LIFE-HISTORIES OF INSECTS 249 



A very large number of animals that live in the water, whether 

 in the sea or fresh water, hatch out from the egg in a larval condi- 

 tion. That is to say, the being which leaves the egg is very 

 unlike the adult in structure and habits, but by growth and a series 

 of accompanying -changes, in time passes over into the adult which 

 is capable of reproducing. These changes constitute the meta- 

 morphosis. In the life-history of land animals such larval stages 

 are rare and indeed hardly exist outside the lusecta and the 

 Amphibia. As we have seen, the egg of a Cockroach gives rise to a 

 young Cockroach which differs but little from the adult and gradu- 

 ally grows into it by a series of small changes, but which never at 

 any time undergoes a long period of profound rest. But if we con- 

 sider the case of a Moth or Butterfly we shall find that the egg does 

 not give rise to an animal resembling a minute Butterfly but to a 

 worm-like larva or caterpillar, which has no wings and in other 

 respects is very unlike the Insect which produced the egg. This 

 caterpillar as a rule eats voraciously and grows rapidly with little 

 change in form until its fourth ecdysis, when a sudden change 

 occurs, and the so-called pupal stage supervenes. In this stage 

 with a few exceptions the animal, now called a pupa (Lat. pupa, a 

 puppet), is motionless and ceases to feed. It may be uncovered and 

 protected only by the hard- 

 ened integument or it may 

 be enclosed in a casing or 

 cocoon. In the case of 

 the Silkworm Moth and 

 some others, this is con- 

 structed of silk. During 

 the pupal stage, the ani- 

 mal undergoes a profound 

 change, many of its organs Fj& 102 Larva of Bombyx mori> the silk . 

 and tissues being broken wornu Life size, 



up and new ones con- 

 structed. When this process is completed the pupa casts its skin, 

 makes its way out of the cocoon and emerges as an imago (Lat. 

 imago, an image) or perfect insect. 



The various orders of Insecta differ in the degree to which 

 metamorphosis occurs. In the Aptera there is no metamorphosis 

 and the development is said to be direct. In Orthoptera and 



