TEXT-BOOK OF ENTOMOLOGY 



This postoral segment at first appears to be one of the thoracic 

 segments, but is afterwards added to the head, though not until 

 after birth, as it is still separate in the freshly hatched nymph 

 (Fig. 4; see also Kolbe, p. 132, Fig. 59, sq. 5). A. Brandt's figure 

 of Calopteryx virgo (PL 2, Fig. 19) represents an embryo of a stage 

 similar to ours, in which the postoral or sixth (labial) segment is 

 quite separate from the rest of the head. The accompanying figure, 

 copied from our memoir, also shows in a saw-fly larva (Nematua 

 ventricosus) the relations of the labial or sixth segment to the rest 

 of the head. The suture between the labial segment and the preoral 

 part of the head disappears in adult life. From this sketch it 

 would seem that the back part of the head, i.e. of the epicranium, 

 may be made up in part of the tergite or pleurites of the mandibular 

 segment, since the mandibular muscles are inserted on the roof of 

 the head behind the eyes. It is this labial segment which in Cory- 

 dalus evidently forms the occiput, and of which in most other insects 

 there is no trace in larval or adult life, unless we except certain 

 Orthoptera (Locusta), and the larva of the Dyticidse. 



The following table is designed to show the number and succession 

 of the segments of the head, with their respective segments. 



TABULAR VIEW OF THE SEGMENTS, PIECES (SCLERITES), AND 

 APPENDAGES OF THE HEAD 



