1909.] NATURAL SCIENCES OF PHILADELPHIA. 29 



The Leg. — The coxa is very closely connected with the pleuron in 

 certain insects, and indeed Miall and Denny, '86, consider that the 

 pleural sclerites are "two basal leg-joints which have become adherent 

 to the thorax." From his embryological studies, Heymons, '99, also 

 adopts this view in designating the "subcoxa" as the basal portion of 

 the leg. Borner, '03, at first considered the pleural sclerites as plates 

 which have become separated from the sternum, but he later adopted 

 Heymons' view. 



The theory that the pleural sclerites are basal leg-joints appears 

 hardly tenable. In those insect larvae which have long, well-developed 

 legs (as for example Corydalis, Carabus, etc.) it is necessary that the 

 muscles have some firm support, and it is doubtless the stimulus of 

 the muscular tension which causes the formation of certain sclerites 

 in the soft integument of the larva. This is certainly a far more reason- 

 able supposition than that the epimeron and episternum would be 

 drawn up from a hard chitinized leg region into a soft pleural region, 

 before the latter region were sufficiently resistant to furnish the needed 

 support for the muscles. In the above mentioned insects, the pleural 

 sclerites first appear near the base of the leg, and it is quite possible 

 that these would appear to arise from the basal region of the embry- 

 onic leg mass, as it is impossible to say just where the leg begins and the 

 pleuron ends in the embryonic stages. There is such a shifting, 

 flattening, and distorting of the parts in those forms upon which 

 Heymons bases his conclusions, that he was deceived into considering 

 that the mesothoracic subcoxa (fig. 16) represents the epimeron and 

 episternum together, whereas, in reality, it represents the mesothoracic 

 episternum, laterale, and perhaps the trochantin. On the other hand, 

 the "pleurit," which he considers as representing the metathoracic 

 pleurites, does not belong to the metathorax at all, but is merely the 

 mesothoracic epimeron (fig. 15, EM"). This mesothoracic epimeron 

 is thrown into a fold by the shifting forward of the region behind it 

 and overlaps the metathoracic epimeron (EM'"), which escaped 

 Heymons' attention altogether. These facts serve to illustrate how 

 easily the embryonic regions may be confused ; and when one takes into 

 consideration that even in the larval stages of the above mentioned 

 insects, the pleural sclerites are first formed so near the base of the leg, 

 it is readily comprehensible that Heymons could have been misled 

 into considering the pleurites as basal leg-joints, since in the embry- 

 onic stages (upon which he bases his conclusions) there is no sharp 

 distinction between the leg and pleural region. 



It is perhaps worth mentioning in this connection that the katepis- 



