hosford: head segmentation of insects. 67 



I. Areas of the External Skeleton of the Head. 



By making a comparative study of the following insects: 

 Orthoptera- — cricket, cockroach, Corydalis (larva and adult), 

 walking-stick, mantis, Dahinia, Orchelimiim, Decticinse, and 

 grasshopper; and Coleoptera — Amblychila, I have made the 

 following observations : 



1. (E. SU.) The Epicranial Suture, though indistinct and 

 small in Dahinia, Orchelimiim, and Decticinse, is present in all 

 of the Orthoptera and can easily be traced in the Amblychila. 



2. (F.) The Front, the first single sclerite between the 

 arms of the inverted Y {E. SU.), is always present. It is en- 

 larged by pushing up of E. SU.; smallest in larva of Corydalis. 

 In the orthopterous forms it includes the paired ocelli and 

 median ocellus when present. The beetle studied has no ocelli. 



3. (CI.) The Clypeus, the second of the single sclerites 

 between E. SU. and the mouth, is sometimes separated from F. 

 by a deep suture, and sometimes seems but a continuation of 

 it, the suture being absent. The point of separation between 

 the two is always to be determined by the invaginations of the 

 anterior arms of the tentorium. 



The clypeus is often divided by a transverse suture into 

 clypeus first and clypeus second. 



The clypeus is really composed of three parts in a transverse 

 row, the part on the median line being C. proper, the lateral 

 ones on the frontal margin being A^itecoxal pieces of the man- 

 dibles. This division is shown especially well in the larva of 

 the Corydalis. They can be located in the other specimens 

 merely by their assumed position. 



4. (L.) The Labrum, upper lip of the mouth, last single 

 sclerite between E. SU. and the mouth, often appears as an 

 appendage, but is really a portion* of one of the head segments. 

 In some cases the markings make it appear as composed of 

 two parts. 



5. (E.) The Epicranium in the forms studied includes the 

 paired sclerites of the skull. These sclerites constitute the 

 sides of the head and that part of the dorsal surface that is be- 

 hind the arms of the epicranial suture (E. SU.). 



6. (V.) The Vertex, the first pair of paired sclerites be- 

 hind the arms of E. SU., the dorsal portion of the epicranium; 

 or that portion which is next the front and between the com- 



