212 A. S. Packard, Jr. on certain Entomological Speculations. 



necessity of assuming that the larva moulted twice over to pass into 

 the pupa state. [See Harris' Insects, etc., p. 577.] Thus, perhaps, as 

 often happens, one mistake has given truth to another, and in stopping 

 one leak, another has been opened."* 



Here Mr. Walsh terms as " certain assertions" what are matters of 

 pure observation with these two authors. He shows that he has 

 never carefully observed an insect through its transformations. He 

 evinces an utter ignorance of the mode of growth of animals, i. e. 

 by the formation of new cells. He contends that insects suddenly 

 moult into the pupa state, as if by a kaleidoscopic process, or by the 

 sudden shifting of theatrical scenery. He denies a well-known fact, , 

 that the Hessian Fly and two other species of Cecidomyia have co- 

 arctate pupae. He forces upon the authors just mentioned, the awk- 

 ward necessity of assuming " that the larva moulted twice over, to 

 pass into the pupa state," which is by no means the case. And 

 finally, ''as often happens" in the theoretical writings of our author, 

 " one mistake has given birth to another, and in stopping one leak 

 another has been opened !" 



Listen first to the statement of Dr. Harris. 



" From the foregoing passages,! lt appears that the transition of the 

 insect, within the flaxseed 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 skiu 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 affected in 

 the same way as in that insect. But the larva of the Hessian fly does 

 not spin a silken web or cocoon like that of the willow gall-fly and 

 some other Cecidomyians ; and it differs from these insects, also, in 

 being finally invested with two skins, the outer one, when detached, 

 serving instead of a cocoon for the included insect, while the inner 



* Loc. eit. p. 562. 



fin which he quotes the direct observation of that most accurate and pains- 

 taking observer, Mr. E. C. Herrick, as follows :—" The process of growth goes 

 on, and. by and L.v. on opening the leathery maggot skin, now a puparium, 

 you find th.' pupa so far advanced thai some of the members of the future Fly 

 are discernable through the scarf which envelopes and fetters it on all sides." 

 In a letter to Harris. 



Again in his article in the Patent office report. ls-U. p. 163, as quoted by 

 Harris on p. 577, Mr. Herrick states: " Within this shell (the flax seed case) 

 the pupa gradually advances towards the winged state ; it contracts in length, 

 hut not in' breadth ; and its skin appears covered with minute elevations. Just 

 before evolution (of the fly), we iind 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." The italic are ours. 



