12 ILLINOIS BIOLOGICAL MONOGRAPHS [244 



i4 

 In the head of Corydalis caudad of the antennae there is a distinct 



ocularium which bears five or six ocelli. This indicates the position of the 



developing compound eyes. In C. bivulnerus the ocelli (Figs. 5 and 6, oc) 



are placed three on each lateral aspect of the head dorsad of the antennal 



fossae. They are usually arranged in the form of a triangle. These ocelli 



are undoubtedly the homologues of the ocelli of Corydalis and represent 



the developing compound eye of the adult. The arrangement, number, 



and position of the ocelli is fairly constant in all of the genera of the family. 



There is only one exception worthy of note; the region bearing the ocelli 



in Scymnus is darkened and slightly chitinized. Two of the ocelli are 



equal in size, while the third is almost twice as large as either of the others. 



In generalized insects the gula is present as a distinct chitinized sclerite 

 extending cephalad from the occipital foramen to the articulation of the 

 maxillae and submentum. It is bounded on its lateral margins by the 

 postgenae. In all of the larvae of the Coccinellidae the gula (Fig. 17, g) 

 is present as a more or less membraneous, rectangular, glabrous area caudad 

 and dorsad of the submentum. 



The internal skeleton of the head of insects is formed by invaginations. 

 It serves undoubtedly to make the head more rigid, to support the soft 

 and delicate parts, and as a place for the attachment of muscles. The 

 entire internal skeleton of the head is known as the tentorium (Fig. 47). 

 It consists of two or three pairs of arms that have been invaginated from 

 the external skeleton. In the more primitive forms there may be only 

 two pairs. In all of the larvae of the Coccinellidae there are three distinct 

 pairs of arms. 



The pretentoria, also known as the anterior arms of the tentorium 

 (Fig. 47, prt), are invaginated on the dorsal aspect of the head near the 

 point where the epicranial arms turn abruptly laterad. 



The supratentoria, sometimes called the dorsal arms of the tentorium 

 (Fig. 47, sup), are invaginated mesad of the antennal fossae and are well 

 developed in the larvae of the Coccinellidae. 



The metatentoria or the posterior arms of the tentorium (Fig. 47, met) 

 are invaginated on the ventral aspect of the head near the articulations of 

 the maxillae. 



In many insects the occipital foramen is divided into two parts by a 

 distinct bridge. This bridge is the corpotentorium. In coccinellid larvae 

 the corpotentorium is not united to form a complete bridge, but the mesal 

 boundaries of the two lobes which ordinarily fuse t6 form the corpoten- 

 torium (Fig. 47, cp) approximate each other very closely on the ventral 

 aspect of the head and are located much nearer the mouth than the occipi- 

 tal foramen. The metatentoria extend dorsad from their point of invagi- 

 nation along the gular sutures toward the occipital foramen and form 

 important landmarks for the identification of the gula. When they 



