11 



lives. These are, the egg, the larva, the pupa and the 

 gianio. The egg is the first stage in the development 

 of a generation, and the larva is the next. The larvae 

 of the butterflies and moths are called caterpillars ; of 

 beetles, bees and wasps, grubs ; and of Hies, maggots. This 

 is the portion of an insect's life when all growth in size 

 takes place. The pupa is the state during which the change 

 takes place, in which the larva is transformed into the final 

 and adult condition of the insect's life ; the wings are formed 

 and the reproductive organs become complete. The pupa of 

 a butterfly is called a chrysalis ; that of a moth is often 

 enclosed in a cocoon. Fig. 10 shows the bean leaf-roller 

 (E uclamus r py^oteus) with larva (6 and c), pupa (d), and 

 adult (a). In the case of insects which have an incomplete 

 metamorphosis, there is not the same distinction between 

 the larva and pupa, as m the case of those in which this is 

 complete. There is no quiescent stage during which the 

 insect transforms, as in the case of the chrysalis of the 

 butterfly. (See Fig. 9.) 



The growth of insects is accompanied by a scries of 

 moults. The chitinous exoskeleton, once formed and hard- 

 ened, is not capable of growth, and it is natural that it 

 should be shed at intervals, when the limbs and organs have 

 increased in size as much as they can. Before the old skin 

 is cast off', there is formed under it another, which is soft, 

 pliant and elastic. As soon as the old one is shed, the new 

 skin is stretched out by the pressure from within, and it 

 then hardens. The exoskeleton, as it now becomes, is fixed, 

 and does not grow any more. The size of the insect is 

 stationary until the next moult, except that the flexible con- 

 nective tissues between the segments are capable of stretch- 

 ing a little. 



The body of a caterpillar, which may be considered 

 a typical insect in the larval condition, is composed of 

 thirteen segments, as follows : the head, which appears as 

 one; the thorax, three; and the abdomen, nine. The segments 

 of the thorax and abdomen are chitinous rings, joined 

 together by means of a flexible connective tissue, which 

 allows for great freedom of movement, and, asalreadvstated. 

 tor a certain amount of growth in size. In most adult 

 insects, it is not easy to distinguish the segments which go 

 to make up the thorax and abdomen, because these are often 

 much modified in accordance with the habits or structure of 

 the insect. 



