NO. 7 THE INSECT CRANIUM SNODGRASS 4I 



the face, the grooves containing the anterior tentorial pits converge 

 toward the bases of the transposed antennae, and are now connected 

 by a transverse groove («'/') between the pits, there being thus estab- 

 Hshed in the adult a complete epistomal sulcus setting off the clypeus 

 from the frons. A comparison with other insect larvae in which the 

 arms of the cleavage line go mesad of the tentorial pits (fig. 10 A. 

 C, G, I) will show that in such cases the epistomal sulcus is either 

 absent or represented only by short lateral grooves containing the 

 pits. On the other hand, when the cleavage lines do not reach the level 

 of the tentorial pits, a complete epistomal sulcus may be present in 

 the larva (fig. loD). Also the sulcus may extend between the 

 tentorial pits when the exuvial cleft does not follow the arms of the 

 obsolete cleavage line, as seen in Vesptda (fig. 14 D) and Xylocopa 

 (F). 



The head transfoi-mation of Ncodiprion from larva (fig. 14 A) to 

 adult (B) shows clearly that the epistomal sulcus of the latter has 

 no relation to the cleavage line of the larva. The interpretation given 

 by Cook ( 1944) in reference to Zaraea amerkana that in the larva the 

 cleavage line of the head is the "clypeofrontal suture" seems, there- 

 fore, quite inconsistent with the facts. The groove appearing in the 

 adult of Ncodiprion that connects the anterior tentorial pits runs 

 between the two sets of facial muscles that are separated by the 

 frontal ganglion, and this groove, therefore, is the epistomal sulcus, 

 or clypeofrontal "suture." The cleavage lines of the larva simply 

 disappear with the transformation to the imago. 



In the wasps and the bees the larval head shows no distinct arms of 

 the cleavage line such as those of the Tenthredinoidea, but the coronal 

 line is always present (fig. 14 C, D, F, CL). This fact would suggest 

 that the exuvial split at ecdysis follows the coronal line alone. The 

 only example of the head cleavage at ecdysis in the higher Hymen- 

 optera here presented, however, is that of Vespa craho (E), in which 

 it is to be seen that the head exuviae are bisected by a median cleft 

 from the occiput to the labrum. Faintly impressed lines present on 

 the head of Polistes (C) and Vespa (D), converging upward from 

 the tentorial pits, are possibly remnants of the unused arms of the 

 cleavage line. The larval head of Polistes (C) resembles the tenthre- 

 dinid larval head (A) in that there is no transverse sulcus connecting 

 the tentorial pits. In the larvae of Vespula (D) and Xylocopa (F), 

 however, this sulcus is present as in the adult of Neodiprion (B) and 

 sets oft" the clypeus from the frons. The manner of ecdysis in the 

 Hymenoptera needs further investigation. 



