1916] Thoracic and Cervical Sclerites of Insects 75 



and it appears very probable that they are detached portions of 

 both the head and prothorax. In some forms such as Forficula, 

 Dolerus, etc., the lateral cervical bears an inward projecting 

 process (Fig. 14, ap). 



In Periplaneta there are two large lateral cervicals on either 

 side of the neck and two ventral cervicals (Fig. 3, Ics, vcs). 

 The lateral sclerites articulate with the head and prothoracic 

 precoxale. This is true of all insects where the lateral cervicals 

 occur except when they are fused with the precoxale and 

 episternum (Fig. 7, Ics). In the latter case they articulate with 

 the head alone (Fig. 12, Ics). The lateral cervical sclerites in 

 Periplaneta articulate with small sclerites attached to the head 

 as shown in (Fig. 3, a). The lateral cervicals very nearly meet 

 in front of the prothoracic verasternite in Periplaneta (Fig. 3, 

 Ics) . The lateral cervical sclerites in Gryllus consist of one large 

 plate on either side of the neck, which probably represents the 

 fusion product of the two lateral sclerites found in the roach 

 and other insects (Fig. 7, Ics). The two ventral sclerites in the 

 roach, have evidently become split into five small sclerites in 

 Gryllus (Fig. 7, vcs). 



There is only one ventral cervical sclerite in Forficula and 

 Capnia, the other having disappeared, while the lateral cervicals 

 in the former are more numerous than in the latter (Figs. 8 

 and 4). Both of these insects have a large, more or less oval 

 sclerite situated directly in front of the prothoracic verasternite 

 (Figs. 8 and 4, prs) , which has been mistaken by several writers 

 for a cervical sclerite. This sclerite is in reality the presternite, 

 which has become detached from the verasternite. In the 

 prothorax of the roach Ecfobia lapponica, the presternite is seen 

 in the process of becoming detached (Fig. 9, prs). 'It has been 

 found, however, in only a few insects. 



The cervical sclerites are quite numerous in the lower 

 insects such as Periplaneta, Gryllus, etc. (Figs. 3 and 7). In the 

 higher insects (Neuroptera, Lepidoptera, Diptera, etc.), there is 

 a tendency for the cervical sclerites to fuse together and increase 

 in size, which becomes more marked in the more specialized 

 forms (Fig. 2, Ics). The cervical sclerites in many Coleoptera 

 have disappeared or have become indistinguishably fused with 

 the prothoracic plates. In some Hymenoptera (Tenthredinidae) 

 the lateral cervicals have become fused with the prothoracic 

 episternum (Fig. 12, Ics). 



