vir] Introduction to Insects 89 
spots. The whole surface is covered with fine hairs. 
The body consists of a distinct head and thirteen 
segments. The head is of a dirty brown colour with 
black spots. Each of the three following segments 
bears a pair of jointed legs. The third, fourth, fifth 
and sixth, and also the last of the abdominal segments 
bear a pair of false legs each. These are simple protru- 
sions from the lower surface of the body (see Fig. 27 b). 
The stage after the egg—in this case the caterpillar— 
is known as the larval stage and the young insects— 
caterpillars—are known as larvae. 
When fully grown the caterpillars usually leave the 
cabbage and wander off to sheltered places where they 
change into the next stage. Here the caterpillar 
forms a silken web-like platform, fixes itself by its 
tail head downwards, or horizontally, also placing a 
silken thread round the middle of its body as additional 
support. Its skin is then cast, and eventually a hard 
body is formed incapable of movement except of its 
tail. This is the Pupa or Chrysalis stage, and is very 
different from the caterpillar (see Fig. 27c). It is about 
an inch long, of a pale green colour, spotted with black, 
and angular. The divisions into head, thorax and 
abdomen can be roughly determined. After about a 
fortnight the adult butterfly comes out. This stage is 
known as the Imago stage. The adult—as is also the 
case with other insects—does not grow, a small fly 
never becomes a large one. 
The front wings of the adult butterflies are white on 
their upper surface with a black crescent-shaped patch 
at the tip of each. The females may be distinguished 
from the males by the presence of two black spots in 
the middle and a small black patch at the hind edge 
