283 [Packard. 



just under the insertion of the wings, on the posterior half of the ring 

 while on the prothorax the peritrenie lies contiguous to and partially 

 under the posterior edge of the vascular tubercle, which in position is 

 exactly homologous 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 dis- 

 tinction 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 more anterior consists of the head and thorax, which 

 are placed closely 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 pupas 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, accompanied 

 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 hymenoptera 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 

 upon 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 destined 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 of the internal organs, which 

 is simply a continuation of the outer tegument, or arthroderm, is, in 

 the process of moulting, sloughed off with that outer integument.* 



Where before the head and thorax together were but little more 

 than one-half as large as the abdomen, now they are conjointly nearly 

 equal in size to the abdomen. (Fig. 3.) The greatest changes have 

 gone on in the two anterior regions of the body. They unitedly tend 



*It remains yet to be proved whether the biliary tubes, salivary glands and inner 

 genital glands and cavities, form exceptions to this rule. 



