576 
DIPTERA. 
Cabell.* Kollar alludes to the unchanged condition of the 
insect within this case, in the European specimens which 
he had examined. f Mr. Westwood makes the following; 
1 b 
remarks upon some from Vienna that were in his possession: 
“ The insects are enclosed in a leathery case, and on open- 
ing them I discovered the larvae 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 puparium . , 
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 “ be- 
coming a hard shell or covering for the chrysalis”; by 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 puparium, “ it is custom- 
ary,” as stated by Messrs. Kirby and Spence, § “ in speaking 
of pupa: of this description, to refer solely to the exterior 
covering.” Agreeably to this common usage, sanctioned by 
the best entomologists 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 contin- 
ued his account of the transformations of the insect. “ The 
* See page 657. 
f Kollar’s Treatise, p. 121. 
t Note in Kollar’s Treatise, p. 121. See also Westwood’s Modern Classification 
of Insects, Vol. II. p. 620. 
$ Introduction to Entomology, Vol. III. p. 258. 
