Mar..9oo.] MeRCER : DEVELOPMENT OF WiNGS IN LEPIDOPTEKA. H 



The Preplpal Period. (Plate III, Figs. 22-25; 27-28. Plate 



IV, Fig. 29.) 

 In all the previous stages of the caterpillar the wings are inside of 

 the body cavity. In this stage they are found upon the outside. I 

 one dissects the wings out in this stage, he finds it necessary to dissect 

 away the body wall before he can get to the wings if he works from the 

 inside as he did in the other stages. But if he takes the expenevice 

 of Swammerdam and plunges the caterpillar into hot water a te^^ 

 times, then carefully takes off the chitinous covering, he will find the 

 wings as external appendages the same as the legs. 



For some time before the last moult, that is betore the larva hangs 

 itself up for the pupal period, the wings are transparent m the body, 

 and their position is recognized only by their accompanying trachea. 

 As the wing becomes gradually opaque it also becomes very much 

 smaller and the contour is irregular and folded. The wings have now 

 disappeared from the interior of the body, but are easily found in their 

 new position by the method given above. 



This change in position takes place in a very short time whde the 

 caterpillar is searching for a place to hang itself up and spinning 

 he button of silk to which it attaches itself. This is a very curious 

 phenomenon, and one that needs explanation Ceroid explains U 

 easily ' ' The germs of the wing ' ' he says ' ' although hidden under 

 the skin have a great tendency to come to the outside." Landois^ 

 who considered the wings as appendages of the tracheal trunk instead 

 If an invagination of the hypodermis, thought that these germ 

 opened away through the muscular bed with their points and tha 

 then tl.e hypodermis withdrew, thereby letting it appear under the 

 form of an evagination of the integument. Weissmann and others 

 have advanced the idea of the breaking down of the l^YPoderm^ o 

 allow the wings to reach the outside. Dewitz does not refer to the 

 taking down of the hypodermis. According to him the o^^ning 

 of the cavity of the invagination is enlarged just enough to gn a 

 free removal of the wing and it remains for some time like a picture 

 n a f ame. Soon the wing becomes free and the hypodermal frame 

 becomes a part of the body wall. Goi^n says, " This theory raise 

 two principal objections. First, it is difficult or ^^^ ^rific of the 

 neripodal cavity to be able in a few hours to enlarge itself without a 

 ea or ent ; in the second place, in order that all of the envelope 

 coiild find a, place upon the thorax it would be necessary that the 



