310 The Ohio Journal of Science [Vol. XVI, No. 7, 



Internal Anatomy. (PI. XX, Figs. 2, 3, 4, 5, 8, 9, 10, 11; PI. 



XXI, Fig. 22). 



In the following discussion of the internal anatomy of the 

 head, those structures previously mentioned will be omitted 

 and only the parts which pertain directly to the internal 

 structure will be considered. 



Tentorium — (Figs. 4, 5). In the heads of all insects there 

 is to be found a definite arrangement of supporting, chitinous 

 structures, which owe their origin to three pairs of primary 

 invaginations of the body wall. The structure itself consists 

 of a system of rod or plate-like bodies, which constitute the 

 tentorium or internal head skeleton. In the Jassid head this 

 skeleton is present, but in some respects it has been modified. 

 The three pairs of arms which compose the tentorium are known 

 respectively as the anterior, dorsal and posterior arms. The 

 anterior arms (i. a.) are invaginated on the cephalo-lateral 

 edges of the clypeus; in the Jassid head this invagination is to 

 be found at the upper corner of the so-called mandibular plate; 

 it persists as an opening and can be distinctly seen in a specimen 

 which has been boiled in KOH. In many insects the points 

 of the invaginations do not persist in the adult. The anterior 

 arms (i. a.) are always associated with the mandibles, and 

 in the Jassid head they are to be found near the articulation 

 of the mandibular setse. The dorsal arms (d. a.) are invaginated 

 beneath the antennee and are easily seen in the head of Delto- 

 cephalus inimicus or any Jassoid. They are always associated 

 with the antennae, and in this case they occupy their normal 

 position. While the invaginations themselves are not readily 

 seen, the arms are quite prominent. The posterior arms (i. p.) 

 are invaginated at the sides of the occipital foramen and are 

 near the attachment of the maxilla. The upper ends of the 

 posterior arms are connected by a chitinous bridge (the max- 

 illary bridge of Muir and Kershaw), which is the body of the 

 tentorium (t. b.). The latter divides the occipital foramen 

 into two parts. 



In the Jassoid head the parts of the tentorium have been 

 modified to a certain extent, but nevertheless they can readily 

 be homologised with the corresponding structures in the Cicada 

 and other Homoptera. From the invagination of the anterior 

 arms, on either side of the head, two small chitinous structures 



