1916] Thoracic and Cervical Sclerites of Insects 69 



finds this region has fused entirely with the coxa and is sep- 

 arated from the epimeron by membrane. He also finds similar 

 conditions in the larval, pupal and adult stages of Trichoptera. 

 It seems more probable however, that the meron is part of the 

 coxa and derived from it, as the condition found in the roach 

 plainly indicates. The roach is also a more primitive insect 

 than the Trichoptera, etc. In some insects (Tipula, Mantispa, 

 etc.) the epimeron is divided into an upper and lower region 

 and the meron is also present. This would probably not be 

 the case if the meron were equivalent to the lower portion of the 

 epimeron (Figs. 1 and 13, m). 



The position of the coxa in its various relations to the other 

 parts of the thorax in different insects, has led to the formulation 

 of various theories from time to time. 



Thus Miall and Denny, '86, from a study of the roach, con- 

 cluded that the sclerites at the base of the leg, represent two 

 basal leg joints, which became attached to the thorax. 



Heymons, '99, in his studies on Nepa designated the sclerites 

 at the base of the leg (episternum, precoxale, etc.) as the "sub- 

 coxa," and adopted Miall and Denny's view, that this region 

 represents the basal portion of the leg. 



Several writers including Hansen, Jourdain, Borner and 

 Henneguy, have compared the styH found on the meso- and 

 metathoracic coxae in certain insects, to parts (exopodite, epipo- 

 dite, etc.) of the crustacean leg. Banks, '93, considered the 

 StyH as vestigial legs and Verhoeff, '02-'04, regarded them as 

 homologous with the coxal organs of Myriopoda. 



Walton, '00, considered the meron as a vestigial leg, but 

 has since retracted this statement. 



Most of the above mentioned theories have already been 

 discussed under the heading. Historical Review, and it will not 

 be necessary to consider them further here. 



Sternum. The term sternum was originally applied to the 

 whole ventral surface of any thoracic segment and is every- 

 where used in this sense. This, of course, prohibits the use of 

 the term sternum for a subdivision of itself, although several 

 writers have used it in both senses and thus have allowed 

 opportunity for more or less confusion. 



The sternum is probably composed of five subdivisions, 

 which vary greatly in size and shape in different insects. In 



