NO. I THE INSECT HEAD — SNODGRASS 1 5 



as pointed out by Walker (1932), is particularly characteristic of 

 carnivorous insects which chase their prey and capture it with their 

 mandibles, of larvae that burrow with their mandibles, as wood-bor- 

 ing beetles, and generally of species that habitually rest on broad sur- 

 faces, or lurk in crevices. 



Again, the mouth parts may be directed posteriorly, as seen in most 

 Hemiptera (fig. 5 C, D). This condition might be termed opisthog- 

 nathous, except for the fact that such insects have a beak instead of 

 jaws. More literally, therefore, they are opisthorhynchotis. Some, 

 such as the cicada (C), in which the beak slopes posteriorly and 

 downward apparently from the neck (Cvx) are termed aucheno- 

 rhynchons. Others, such as the aphids (D) that hold the beak when 

 not in use close against the undersurface of the body, are termed 

 sternorhynchous. Since the beak of the aphid must be directed down- 

 ward for feeding, it is evidently turned backward for convenience 

 when not in use. 



III. THE SO-CALLED "SUTURES" AND THE SURFACE AREAS 



OF THE HEAD 



The cuticle of the insect head wall is marked by various impressed 

 lines that divide the cranial surface into specific areas. The early 

 entomologists, being acquainted with vertebrate anatomy, naturally 

 saw in the areas of the insect head a likeness to the centers of ossifica- 

 tion in the vertebrate skull united along sutures. It was a simple 

 matter then to give names to the supposed sclerites and sutures of the 

 insect cranium. We still use these same names, but we now realize 

 that the sclerotization of the head cuticle is continuous, and that the 

 so-called "sutures" are mostly lines where the cuticle has been in- 

 folded to form internal strengthening ridges or to give attachment 

 to muscles. The external grooves, if we must have a Latin name for 

 them, are better termed sulci. Strenger (1942, 1950, 1952) has 

 strongly emphasized the functional significance of the cranial sulci 

 (though she calls them Nahte) in that they form internal ridges for 

 strengthening the head wall along lines of mechanical stress. The 

 same applies to most of the "sutures" in other parts of the insect 

 skeleton. Scientific terms should express facts rather than perpetuate 

 errors. When errors become chronic, however, they are hard to eradi- 

 cate. 



There are, of course, always exceptions to any general rule. In 

 some insects there is a true median suture on the under side of the 

 head where the extended lateral walls have grown together. Also, 



