170 THE SHORTER SCIENTIFIC PAPERS 



Walcott (1911) calls attention in the shale surrounding 

 the impression of Worthenella may have something to do 

 with the problem. Here again one must await additional 

 material which will throw light upon the subject. 



In the Lepidoptera the arrangement of the various 

 areas as illustrated by Cossus cossus, one of the large 

 moths, is not far removed from the similar areas as rep- 

 resented by the typical segment of the insects. Two 

 developmental changes are to be noted, the first of which 

 may, however, represent a more primitive condition than 

 exists in other orders, namely, the extreme development 

 of the propteron to form the so-called tegula or para- 

 pteron at the base of the mesothoracic wing. The second 

 change exhibits the tendency of the sternum to extend in 

 a posterior lateral direction over the episternum, so that 

 the latter is apparently cut off from the coxon. Such a 

 development is present in many other representatives of 

 the insects. 



The Coleoptera, as represented by the metathorax of 

 Harpalus calignosus Fab., do not at a casual glance indi- 

 cate any pronounced similarity with the arrangement of 

 the sclerites as shown in the typical segment. This is 

 largely due to the dorso-ventral compression of the body 

 with the resulting distortion of the parts. The tendency 

 of the sternum to develop as in the Lepidoptera is partic- 

 ularly noticeable, while the coxal groove for the reception 

 of the femur, particularly characteristic of the metacoxae 

 in the Coleoptera, tends to render the coxon-meron suture 

 obsolete, particularly at the distal end. 



Many other representatives of the insects or of the 

 Chilopods or the Symphylids could be noted where the 

 same typical form is indicated. In representatives of the 

 Apterygote insects, like Machilis, Campodea, Japyx or in 

 the Protura, the pleurum-appendage area apparently 

 represents a more specialized development of the parapo- 

 dium than in the Pterygote insects. To those who have 

 long held to the opinion that the "Thysanurans" are rep- 

 resentative forms from which the winged insects have 

 evolved, the implied conclusion will seem a heresy. While 

 it is true that one finds many characters in the Machilid 



