DIPTERA. 459 



within this "leathery" outer skin of the larva, and of all its 

 subsequent changes. While this change of the color and 

 texture of the skin is going on, the body of the insect, as re- 

 marked by Mr. Herrick, "gradually cleaves from the dried skin, 

 and, in the course of t\vo or three weeks, is wholly detached." 

 In a letter, dated February 21, 1843, he alludes more explicitly 

 to the condition of the insect, in these words. " In two or 

 three weeks after this change of color, the animal within be- 

 comes entirely detached from the old larva-skin, and lies a 

 motionless g-i-ub." Accordingly, when this dried skin or flax- 

 seed case is opened, the insect will be found loose within it, 

 and still retaining the maggot form, as stated by Mr. Herrick, 

 Mr. Worth,* and Professor Cabell.f KoUar alludes to the 

 unchanged condition of the insect within this case, in the 

 European specimens which he had examined. J Mr. West- 

 wood makes the following remarks upon some from Vienna 

 that were in his possession. " The insects are enclosed in a 

 leathery case, and on opening them I discovered the larvte 

 shrivelled up and dead." § Referring to Mr. Say's account of 

 the Hessian fly, and its flax-seed case, Mr. Westwood says, 

 "it is not described in what manner this case is formed." That 

 it really consists of the loosened outer skin of the maggot is 

 evident from its shape and structure. It has nearly the same 

 form and size, is convex on both sides, and retains traces of 

 the former segments in the transverse lines wherewith it is 

 marked. This flax-seed shell has been correctly called a pupa- 

 rium or pupa-case, because the pupa is subsequently matured 

 within it. Dr. Chapman repeatedly alludes to the pupa, or 

 chrysalis as he calls it, and to "the outward coat" of the larva 

 "becoming a hard shell or covering for the chrysalis;" by 



* Mr. James Worth, writing on this insect in 1820, remarked that " as soon 

 as it changes to the flax-seed color, by rolling it lightly with the finger, the tegu- 

 ment can be taken off ; the worm will then appear with a greenish stripe through 

 it, which is evidently the substance extracted from the plant." ('* American 

 Farmer," Vol. II., p. 180.) 



t See page 443. 



% Kollar's "Treatise," page 121. 



§ Note in KoUar^s " Treatise," p. 121. Sec also Westwood's " Modern Clas- 

 sification of Insects," Vol. II., p. 520. 



