86 Mr. A.S. Packard on the Development 
tions here recorded were made, our attention was drawn* to this 
part. At this period the thorax is one-third smaller than in the 
pupa. The position of the three thoracic spiracles can be easily 
discerned. On the two posterior rings of the thorax they are 
seen situated in their respective “ peritremes ” (Audouin), which 
pieces lie at the base and just under the insertion of the wings, 
on the posterior half of the ring, while on the prothorax the 
peritreme lies contiguous to and partially under the posterior 
edge of the vascular tubercle, which in position is exactly homo- 
logous to that of the wings. 
It is thus demonstrated that the wings grow forth, first as 
vascular sacs, through the arthroderm, just above the line of 
spiracles, and at the line of juncture of the lower edge of the 
tergite and upper edge of the upper pleurite or epimerum; 
while, on the other hand, the limbs grow out through the line 
of juncture of the sternite and the lower pleurite or episternum. 
In what may be termed the third stage (fig. 3), though the 
distinction is a very arbitrary one, the change is accompanied 
by a moulting of the skin, and a great advance has been made 
towards the pupa form (fig. 4). There are seen to be two 
distinct regions to the body—the anterior, consisting of the 
head and thorax, which are placed close together, and the 
abdomen, which is separated from the rest of the body by a 
deep constriction. We cannot fail to be at least reminded of 
the biregional Crustacean—an analogy which Oken has called 
attention to, and which has been successfully used by that 
author in comparing the pupe of Insects with Crustacea. 
At this period the mode of sloughing of the larval skin is well 
shown. Instead of the violent rupture of the skin at one point 
on the tergum of the thorax, as in the majority of insects, ac- 
companied with the great exhaustion consequent on the act, 
which makes the operation a perilous one to most Insects and 
Crustacea, in this species (and most probably all the Hymeno- 
ptera which at this stage have a soft tegument) the skin breaks 
away gradually, in shreds, from the tension due to the unequal 
growth of the different parts of the body. Thus, after the skin 
beneath has fully formed, shreds of the former skin remain 
about the mouth-parts, the spiracles, and anus. Upon pulling 
these, the lining of the alimentary tube and trachee can be 
drawn out, sometimes, in the former case, to the length of 
several lines. As all these internal systems of vessels are des- 
tined to change their form in the pupa, it may be laid down as 
a rule, in the moulting of Insects and Crustacea, that the lining 
* Proceedings Essex Institute, vol. iv., ‘The Humble Bees of New 
England and their Parasites,’”’ &c., April 23, 1864, p. 3, note, 
