2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 10/ 



deceptive, what appears as reality to one may be a mirage to another. 

 At best, morphological interpretations can be deduced only from 

 circumstantial evidence, and evidence is not ci re uiustani'isd if it is 

 one-sided. 



Students of entomology have long beeii taught that one of the most 

 important structural features of the insect head is a Y-shaped line on 

 the face called the "epicranial suture." Now a paper appears (Du- 

 Porte, 1946) in which it is asserted that this "suture" has no structural 

 significance at all, being merely a line of weakness in the head wall 

 where the cuticle splits at ecdysis, with its arms taking quite different 

 courses in dififerent insects. At the same time the same idea had been 

 elaborated in the manuscript and drawings of the present paper. The 

 two papers are in entire agreement concerning the "epicranial suture" ; 

 in other ways they are not completely in accord. DuPorte discredits 

 the value of muscle attachments as criteria for determining homologies 

 of parts in the exoskeleton ; he says, "the known inconsistency of 

 muscle origins throws doubt on their value in determining the ho- 

 mologies of the facial sclerites." However, one unreliable member of 

 a class does not discredit the integrity of all the others. On the face of 

 the insect are attached two groups of muscles, separated by the frontal 

 ganglion and its brain connectives. There is no known irregularity 

 in the relation of these muscles to the facial wall of the head, those of 

 one group never invade the territory of the other group. Wherever 

 the claim is made that there has been a shift in the origins of these 

 muscles it will be found that the claimant has merely changed the 

 name of the external part on which the muscles are attached. The 

 writer, therefore, contends that the facial muscles of the insect head 

 arc reliable criteria for determining the homologies of the surface 

 parts of the cranium. The frontal ganglion, moreover, is an important 

 landmark in the fundamental anatomy of the head, and the structure 

 of the head is not to be understood from a study of its superficial 

 features alone. A man may be characterized by the wrinkles on his 

 face, but probably there is an underlying reason for the wrinkles. 



I. GENERAL DISCUSSION 



The cranium of an insect is the sclerotized cuticle of the head. In 

 discussing sutures it must be understood that an anatomical "suture," 

 according to the literal sense of the word (from L. suere, to sew), 

 should be a line along which two parts have united without obliterat- 

 ing the evidence of their union. The best examples of anatomical 

 sutures, except those made by surgeons, are the irregular lines of 



