122 



INTRODUCTION TO ZOOLOGY. 



may conjecture that they are commonly destroyed iu 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 destruction 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 

 larva? 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, 5 that 545 flies 

 of the same species were produced 

 from four chrysalides of a but- 

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

 transmigrated into that of 545 others.'! 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 l'"J 



* Intr. to Entomology, vol. i. page 266. All the varieties of the turnip 

 and cabbage belong to the genus Brassica. 



f Westwood, vol. ii. page 145. 



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



The three 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. 



