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 pupae 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 diff'erent 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 pulhng 

 these, the lining of the alimentary tube and tracheae 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. 



