254? Pteromali parasitic on M.uscce "within Vhalcena, 



larvae, and of depositing their eggs beneath the surface : the 

 females of the iliuscae, on the contrary, have no such appara- 

 tus, but merely place their Q^g on the surface of the skin, to 

 which it adheres by means of a glutinous matter exuded with 

 it. I must here, however, mention that the learned authors 

 of the Introduction to Entomology have (vol. i. p. 345.) the fol- 

 lowing sentence : — " Some ichneumons, instead of burying 

 their eggs in the body of the larvae that are to serve their 

 young for food, content themselves with glueing them to the 

 skin of their prey, which the young grubs pierce as soon as 

 hatched." Now, I by no means imagine that such a sentence 

 would have found its way into so correct a work without the 

 best authority ; yet, as in no instance in which I have found 

 the egg thus attached has the larva produced any other than 

 a dipterous parasite, I think we may fairly conclude that 

 piercing and glueing are the general and distinctive rule 

 or habit of each particular tribe ; and the fact asserted by 

 Messrs. Kirby and Spence an exception to the rule. 



The egg of the ikfusca, which, I may remark, I have always 

 observed to be placed on the neck of the larva, the only part 

 from which the annoyed insect could not remove it, is very 

 conspicuous to an observer ; and experienced collectors of 

 Lepidoptera, when they find the larva of a rare species with 

 this egg attached, make a practice of removing it, and the larva 

 will then thrive and come to perfection. With the egg in 

 this situation, thus easily visible to the human eye, we can- 

 not wonder that the active and instinct-guided Pteromalus 

 should discover it; nor does it appear an improbable suppo- 

 sition that the little creature seizes this opportunity of piercing 

 the shell with her oviduct, and depositing her egg amidst its 

 contents. So that the larva of the Musca, as soon as hatched, 

 in burying itself in the fleshy larva of the i?6mbyx, is com- 

 pelled to carry with it a horde of insidious parasites, which, 

 although they interfere not with the due performance of its 

 appointed work of destruction, yet in the end so weaken it 

 that it never arrives at perfection. Thus the ^ombyx and 

 ikfusca, both excessively voracious tribes, perform the task 

 allotted them by Providence ; yet are by this minute creature 

 prevented from reproducing their species, whose increase, 

 unchecked, would speedily depopulate the earth. The ques- 

 tion as to the difficulty which so small an insect would 

 experience in piercing a substance so hard as the egg-shell 

 of the Musca, may be at once answered by the fact that 

 many species of the same tribe [Platygaster ovul5rum is one 

 instance, see Vol. III. p. 452.] are known to be parasitical on 

 the eggs of butterflies, in which they have been deposited by a 



