122 



INTRODOCTION TO ZOOLOGT. 



may conjecture that they are commonly destroyed in some 

 such proportion — a circumstance which will lead us thankfully 

 to acknowledge the goodness of Providence, which, by pro- 

 viding such a check, has prevented the utter destniction of 

 the Brassica genus, including some of our most esteemed and 

 useful vegetables."* 



It is worthy of remark that the caterpillar thus attacked 

 continues to eat and apparently to enjoy life as usual. The 



larva placed within it avoids the 

 vital parts, until the period for 

 its own liberation or change of 

 state has arrived; and it has been 

 ascertained that many of these 

 larvae are, in like manner, preyed 

 upon by Ichneumons still more 

 minute than themselves. 



" The development of these 

 parasites within the bodies of 

 other insects was, for a long time, 

 a source of much speculation 

 amongst the earlier philosophers, 

 who conceived it possible that 

 one animal had occasionally the 

 power of being absolutely trans- 

 formed into another. Thus, 

 Swammerdam records, as ' a thing 

 very wonderful,' that 545 flies 

 „. „, ^ . of the same species were produced 



Fig.107.— Ichneumon.? i r i e i. . 



from four chrysalides or a but- 

 terfly, ' so that the life and motion of these seem to have 

 tran-miigraied into that of 545 others.'t How much greater 

 would have been the astonishment of this ardent and laborious 

 naturalist, could he have seen 20,000 of these minute Ichneu- 

 mons issue from the chrysalis of a goat-moth, a number which 

 one author regards as a 'moderate computation!' "J 



■ Intr. to Entomolopjy, vol. i. paRo 266. All the varieties of the turnip 

 and cabbage belong to the genus Brassica. 



■f Westwood, vol. ii. page 145. 



j: Moses Hams. Vid. Westwood, vol. ii. page 9. 



§ The tliree thread-like appendages at the extremity of the abdomen, 

 in figure 107, consist of the ovipositor, and two filaments between which 

 it lies, as in a sheath, when not in use. 



