460 INSECTS INJURIOUS TO VEGETATION. 



which we perceive that he was acquainted with the origin and 

 office of the one and the condition of the other. But as the 

 true figure of the included insect is concealed, and cannot be 

 determined without opening the pupariurn, "it is customary," 

 as stated by Messrs. Kirby and Spence,* "in speaking of pupae 

 of this description, to refer solely to the exterior covering." 

 Agreeably to this common usage, sanctioned by the best ento- 

 mologists of our time, the flax-seed case, or puparium, has 

 been commonly denominated the pupa, even by such writers 

 as Mr. Say, to whom the real nature of its contents must 

 have been well known. 



In the letter before mentioned, Mr. Herrick thus continued 

 his account of the transformations of the insect. " The pro- 

 cess of growth goes on, and, by and by, on opening the leathery 

 maggot-skin, now a puparium, you find the pupa so far ad- 

 vanced that some of the members of the future fly are discern- 

 ible through the scarf which envelopes and fetters it on all 

 sides." In his observations communicated to the Commis- 

 sioner of Patents in 1844,j he referred to the same process in 

 the following words. " AVithin this shell (the flax-seed case) 

 the pupa gradually advances towards the winged state; it 

 contracts in length but not in breadth; and its skin appears 

 covered with minute elevations. Just before evolution (of the 

 fly), we find the pupa invested in a delicate membrane or 

 scarf, which not long previous was its outer skin, through 

 which many parts of the future fly may be distinctly seen." 

 From the foregoing passages, it appears that the transition 

 of the insect, within the flax-seed case, from the form of a 

 larva or maggot to that of a mature pupa, takes place only 

 a short time before its final transformation to a fly, that is, 

 towards the end of April or beginning of May ; and that the 

 scarf or proper skin of this pupa is the same as that wherein 

 the body of the insect had been previously enveloped. In this 

 respect, the Hessian fly agrees in its transformations with the 

 willow gall-fly; and doubtless the transition in question is 

 effected in the same way as in that insect. But the larva of 



* «' Introduction to Entomology," Vol. III., p. 258. t Report, p. 163. 



