SOME ASPECTS OF MORPHOLOGY 3 



which it has not been previously necessary to consult in connection 

 with entomology at all. The future burden of the worker in 

 insect physiology of keeping pace with this literary growth seems 

 likely to become increasingly difficult for this reason. One 

 result from this increase in physiological knowledge seems to be 

 that the morphologist will become better able to develop his 

 subject, since it will be in the light of increased acquaintance 

 with basic functions. Growth of physiological knowledge, also, 

 is likely to involve the re-examination of many features of the 

 minute structure of insects, with possibilities of interpretations 

 being made from another angle of vision. In connection with the 

 foregoing remarks, reference needs to be made to an introductory 

 manual of insect physiology by Wigglesworth (1934). It 

 formulates what is virtually a new subject and co-ordinates 

 much scattered information not readily accessible or easily 

 evaluated. 



In order properly to appreciate the morphological significance 

 of a good deal of insect structure it is necessary to look outside the 

 limits of entomology. While insects, as a class, show a funda- 

 mental organisation common to the Arthropoda, their own basic 

 characters have been evolved by a long and complex process 

 of modification. The morphological interpretation of these 

 characters is essentially a study of homologies, which is hampered 

 owing to lack of evidence as to the course taken by insects in 

 their evolution. While a number of writers claim that the 

 origin of these creatures was either in common with that of the 

 Myriapoda, or from some individual class among that assemblage, 

 other writers bring forward reasons suggesting derivation from 

 an early crustacean type. On the whole, both anatomically and 

 physiologically, insects appear to show a balance of characters 

 favouring the idea of descent frorn a myriapodan rather than 

 from a crustacean prototype (Imms, 1936). This contention 

 forms the basis upon which some of the more general morphological 

 deductions made in this chapter are founded. 



In the present chapter the following aspects of morphology are 

 discussed: (1) the segmentation of the head; (2) the wing 

 venation ; and (3) the metameric appendages. 



1—2 



