36 ON THE ANATOMY OF THE FLY. 



degrees of metamorphosis, especially the presence or absence of 

 imaginal discs in the larva, as suggested by Dr. "Weismann ; or 

 upon the manner in which the head is articulated with the thorax, 

 But until the types of other families have received the same 

 attention as the fly, nothing certain can be said upon the subject. 



In conclusion, it may not be out of place here to make a few 

 observations on the position of the insectain the animal kingdom. 

 The highest insects should probably be regarded as the highest 

 members of the annulose type ; which is apparently so distinct 

 from the vertebrate type that they cannot be compared with each 

 other ; for my own part I confess that I see no evidence of in- 

 feriority of type in either case, the structure of insects is as com- 

 plex and their organs are as perfectly differentiated as those of the 

 vertebrata. Professor Huxley has very ingeniously compaired 

 the embryonic forms of the vertebrate and invertebrate types* and 

 supposes the nervous system of the insecta to be homologous with 

 the sympathetic system of vertebrates, and that the cerebro -spinal 

 nervous system and neural canal are added in the latter ; such 

 can hardly be the case if my observations on the nervous system 

 of insects are correct, as they have also two distinct nervous 

 systems. Even if such an homology should be substantiated, which 

 appears unlikely, the supposition that the alimentary canal ter- 

 minates anteriorly by a neural instead of a ha3mal flexure would 

 not explain the different development of the embryo from the 

 entire surface of the yolk, and the fact that all the organs of man- 

 ducation, prehension, locomotion, and the external organs of gen- 

 eration, originate from the lateral appendages of the various 

 segments. No homologies can be traced for any of these organs 

 between the insecta and vertebrata. 



Introduction to the classification of animal?, 



