WELLMAN: A StUDV OF THE PROTHORAX OF BUTTERFLIES. I39 



thorax and is probably liomologous with the postscutelliim of the 

 other segments. The parts of the pleura and sternum are plainly dif- 

 ferentiated; the sternum and episternum forming a broad band be- 

 neath; the episternum reaches to the lower edge of the dorsal lobes. 

 The suture between the sternum and episternum, while not distinct is 

 yet evident, the upper part of the episternum is somewhat tumid, 

 resembling the dorsal lobes in shape and surface. That part of 

 the membrane lying just above the cox;i3 is partially chitenized 

 in this form and corresponds to the epimeron of the other thoracic 

 segments. When one examines the form of the epimeron in the 

 wing-bearing segment there is no doubt that the membranous part 

 of the prothorax, lying between the other sclerites and the meso- 

 thorax is homologous with the epimeron, for that sclerite is always 

 only partially chitenized or, at most, always lies adjacent to the area 

 of delicate membrane surrounding the wing articulation. See fig. II. 



The next group shows a considerable variation in the structure of 

 the lobes and so may be arranged into three subclasses. The general 

 appearance, however, is much the same throughout, the prothorax 

 being characterized by the broad membranous part which joins, 

 unbroken, with the membrane surrounding the wing of the meso- 

 thorax, that part next the wing being covered by the patagia of the 

 mesothorax. 



The first subclass of this group is repre- 

 sented by Colitis cceronia, fig. IV. The pro- 

 thoracic lobes are small and are situated 

 on the extreme lateral border of the pro- 

 thorax. They are very dark in color and show fine tuberculations. 

 The membranous part of the prothorax drops away abruptly from the 

 lobes and scutellum, thus leaving them prominent; the membrane 

 attached to the lateral extremity of the lobes rolls backward slightly 

 along the anterior margin of the prothorax, forming a narrow ridge 

 beneath the lobes, and in front of this fold is the narrow chitenized 

 band or collar formed by a lateral extension of the scutellum which 

 it joins between the lobes. The sternum and episternum are coalesced 

 into a narrow band which does not reach the dorsal area by some 

 distance; this is one of the important characteristics which separate 

 this group from the preceding, and holds throughout the three sub- 

 classes with only slight variations in form. The sternum meets the 

 anterior chitenized band of the dorsum about midway on the plurae, 

 so completing the chitenized ring which gives strength and form to 

 the prothorax. 



