284 HACHIRO YUASA 



less extent than the dextral. There is also a difference in the 

 number of extensions on the epigusta. All these peculiarities 

 seem to be of secondary importance, since their presence can be 

 explained by the asymmetrical conditions of the mandibles 

 which, when brought together, leave an irregular space for the 

 parapharynx to fill. The nature of the lateral lobes is more 

 difficult to explain. They are the 'paraglossae' of the older 

 writers, and correspond to the 'maxillulae' of Hansen ('94) and 

 'superlingue' of Folsom ('00). Berlese ('06) considers the 

 entire parapharynx, including the lateral lobes, as derived from 

 the labium, and thus disagrees, like many others, with Folsom's 

 view concerning the origin and nature of these lobes of the 

 hypopharynx. Carpenter ('16) figures the labium of Isolepisma 

 bisetosa with a 'maxillula' which simulates the conditions found 

 in Orthoptera and Euplexoptera. 



SUMMARY 



1. This study on the comparative anatomy of the head and 

 mouth-parts of orthopteran insects has resulted in establishing 

 the homology of all of the structures present in generalized and 

 specialized Orthoptera, and in elucidating the hitherto but 

 little studied structures, the propharynx and tentorium. Ex- 

 cepting variations in size, shape, and other superficial differ- 

 ences, not of primary importance, all of the structures examined 

 reveal a remarkable uniformity in their general organization and 

 at the same time indicate the trend of evolutionary processes 

 which are responsible for the apparent gradation in specialization 

 manifested by these structures. 



2. Since morphology offers fundamental evidence for the deter- 

 mination of phylogeny, a word may be added, with due appre- 

 ciation of the limitation of the data at hand, as to the probable 

 genealogical relations of the insects under consideration. Briefly 

 stated, the anatomical evidences presented in this paper show 

 that the Blattidae is the most generalized; that the Mantidae is 

 closely related to the Blattidae, that the Gryllidae follows the 

 Mantidae, although it is not likely to have developed directly 



