252 HACHIRO YUASA 



intimate a relation between the segmentation and the sclerites 

 cannot be shown." More recently the mouth-parts of the cock- 

 roach were studied by Mangan ('08) and Bugnion ('13, '16). 



In spite of the fact that an immense amount of valuable infor- 

 mation is found in the more comprehensive works on general 

 entomology, notably Kolbe ('89), Packard ('98), Henneguy ('04), 

 Berlese ('06), and Schroder ('12), and, contrary to the general 

 impression that the external anatomy of insects in general and 

 especially of the more common insects such as Orthoptera has 

 already received sufficient attention from morphologists, it is sur- 

 prising, when the subject is scrutinized a little more closely, to 

 find how few studies of homology have been attempted by the use 

 of a series of forms. The possible exceptions in America are 

 the successful attempts to homologize the wing veins of different 

 orders by Comstock, Needham, MacGillivray, and others and 

 the careful investigations of Crampton ('09, '14, '17), Snodgrass 

 ('09, '10), and Peterson ('16) on the different regions of the insect 

 body. The confusion in the terminology used by insect morphol- 

 ogists and the greater confusion of the anatomical terms now cur- 

 rent among taxonomists, particularly among speciaUsts interested 

 exclusively in restricted groups, amply justify attempts to in- 

 vestigate and in many cases to reinvestigate the more funda- 

 mental structures of insects. 



The following pages present a resume of a detailed study of the 

 salient characteristics of the external anatomy of the head and 

 mouth-parts of the generalized biting insects as represented by 

 typical species belonging to the orders Orthoptera and Euplex- 

 optera. Particular attention was given to structures hereto- 

 fore little studied— the prepharynx and tentorium. This study 

 was undertaken under the supervision of Prof. Alex. D. Mac- 

 Gillivray, of the University of Illinois, and to him I extend my 

 sincere thanks for suggestions and encouragement and for the 

 permission to use his unpublished terminology^ and forthcoming 

 outline for the study of insect anatomy. This outline proved 

 most valuable and indispensable as a guide. 



2 The new terms used in this paper are defined in the following pages. On 

 pages 285-286 they are tabulated in their relations to other parts. 



