VEGETABLE PLANTS. 73 



whose depredations the cabbage is likely to 

 suffer is the white cabbage butterfly, which has 

 been in this country but a few years, and is the 

 parent of the much detested green cabbage 

 worm. For a year or two after its advent in 

 this country it caused general and almost com- 

 plete destruction. Now it injures the plants 

 to some extent, but by no means so severely as 

 formerly. The reason for this is that its natu- 

 ral enemies have also become numerous enough 

 to keep it in check. Like all other insects, 

 there are three stages to its existence viz., the 

 perfect insect, which is the butterfly ; the cater- 

 pillar, or green worm, in which form it is most 

 destructive ; and third, the chrysalis, or pupa 

 state, in which it is dormant, and undergoes 

 the change from worm to butterfly. When in 

 this state, and to all appearances lifeless, in 

 which condition it passes the winter, it is 

 sought by a small parasitic fly, which punctures 

 its skin and lays within its shell a number of 

 small eggs. These soon hatch out into little 

 white maggots, which eat the inside entirely 

 out, leaving only a hollow shell. We have ex- 

 amined dozens of these chrysalides in early 

 spring which are to be found on the sides of 

 buildings, fences, stones, or any rubbish near 



