NO. 7 THE INSECT CRANIUM SNODGRASS 9 



end of each temporal ridge a short branch (d) extends mesally along 

 the frontal arm of the persisting nymphal line of ecdysis (CL). The 

 exuviae of a nymphal mantis (F), however, shovi^ that in the im- 

 mature insect the facial ridges are much less developed than in the 

 adult ; there is here no trace of the branches from the temporal ridges 

 invading the arms of the cleavage line, and even in the last nymphal 

 stage the temporal sulci themselves (F, ts) do not reach the latter. 

 In the first instar nymph (E) the temporal sulci end far short of the 

 arms of the cleavage line, which are pale soft tracts of the head cuticle 

 leading directly to the eyes. The frontal arms of the cleavage line are 

 thus unencumbered in the nymph; at ecdysis (F) the frontal splits 

 extend through them unobstructed, and furthermore, at least at the 

 final ecdysis, they cut through the middle of the compound eyes (E). 



The structure in the mantis on which Ferris bases his concept of 

 "the great suture" is thus seen to be one that pertains only to the 

 imago, which, being done with moulting, can undergo a structural 

 remodeling without regard to ecdysis. If the apparent continuity of 

 the cleavage lines and the temporal sulci in the adult mantid were real 

 and of such fundamental structural importance as Ferris contends, 

 the unity of the lines should be all the more evident in the nymph. 

 Among other species of insects given by Ferris to illustrate his "great 

 suture" he nowhere is able to find an actual continuity between the 

 "postfrontal sutures" and the "temporal sutures," and, as will be 

 shown later, in his discussion of the head of the symphylid Scuti- 

 gerella he is forced to compose a "great suture" from ingredients that 

 are not sutures at all and have no relation to one another. 



The area below the so-called "postfrontal sutures," or arms of the 

 cleavage line extending laterad of the antennal basis (fig. iD), is 

 regarded by Ferris (1942) as the "frons," or later (1943) as the 

 "antennal segment"; but when the arms go downward on the face 

 between the antennae (F, G), as they do in most holometabolous 

 larvae, they are together identified as the "clypeofrontal suture," and 

 the facial area embraced by them is interpreted as that of the clypeus 

 extended upward on the face. Yet if the cleavage lines were deleted 

 (fig. I B) there would be no evident differences in the structure of 

 the head in the two cases. The cranial muscles have always the same 

 relative distribution, as is amply shown by Cook (1944) in his com- 

 parative study of the labral and clypeal muscles in the principal orders 

 of insects, though Cook follows the Ferris interpretation of the 

 skeletal areas of the head. The facts represented diagrammatical ly on 

 figure I (C-G) show that the frontal arms of the cleavage line simply 

 take any position in the otherwise unoccupied spaces between the 



