THE INSECT CRANIUM AND THE "EPICRANIAL 

 SUTURE" 



By R. E. SNODGRASS 



Collaborator, Bureau of Entomology and Plant Quarantine, 

 U. S. Department of Agriculture 



CONTENTS 



Page 



Introduction I 



I. General discussion 2 



II. Examples of the ecdysial cleavage line of the head 13 



Apterygote insects 13 



Ephemeroptera and Plecoptera 14 



Odonata 14 



Dermaptera I4 



Orthoptera 16 



Hemiptera 18 



Anoplura 22 



Coleoptera 24 



Neuroptera (Megaloptera and Planipennia) 28 



Mecoptera 31 



Trichoptera 32 



Lepidoptera 33 



Diptera 34 



Hymenoptera 39 



Symphyla 42 



III. Summary 44 



Abbreviations used on the figures 47 



References 49 



INTRODUCTION 



The structure of insects presumably remains the same for long 

 periods of time. A reading of entomological texts and papers, how- 

 ever, might give the impression that a rapid change has been going on 

 in insects even during the last few years. The evident stability of the 

 insect structure as compared with the diversity in the written accounts 

 of it simply illustrates the difiference between anatomy and mor- 

 phology. Anatomy refers to the facts of structure, morphology is our 

 interpretation of the facts or what we think about them. Anatomy 

 is unchangeable, except by the slow processes of natural evolution ; 

 morphology, on the other hand, changes with each generation of 

 morphologists, or as often as any morphologist changes his mind or 

 thinks he sees a new light on an old subject. Sometimes the light is 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 107, NO. 7 



