392 ON INSECT ANATOMY. 



belongs to a more recondite chapter of biology as a portion of the 

 higher generalisations of developmental law ; and though it affords 

 truly wonderful and instructive glimpses into insect evolution, is 

 misapplied in the limited uses of classification. 



But other classifications founded with more success on permanent 

 external features demonstrate the value of insect anatomy. In parti- 

 cular, the anatomy of the mouth and accessory appliances has proved of 

 great importance. Por its masticatory or suctorial character has a 

 definite relation to the insect's nutritive organs, its food and life 

 habits. Then, as secondary characters the presence or absence of 

 wings with their number and arrangement, together with difference 

 of antennae, limbs and feet, offer many distinctions which have a 

 direct connection with the modes of life of each species so 

 characterised. In all classifications the various life habits afford 

 natural and simple means of characterising insects, obviously, 

 because it is [more easy to observe these than to determine the 

 anatomical peculiarities with which they are associated. 



It is, therefore, not surprising that the nervous system plays so 

 little part in any scheme of insect classification. The homo- 

 gangliate character assigned to insects, in common with other 

 divisions of articulata, admits indeed of considerable variation ; but 

 the infinite diversity of external characters of the insect's body 

 is not accompanied by such obvious differentiations of nerve 

 organs as would serve for purposes of classification. It cannot be 

 doubted, however, that all the powers and faculties of insects 

 expressed in their life habits, stand in close connection with the 

 degree in which cephalic thoracic or abdominal ganglia are 

 developed. From the relation, size, 'and complicity of the nerves 

 and Ganglia of these three divisions and of the sensory organs, the 

 probable conditions of the insect's existence may be fairly premised 

 and the particular phase of metamorphosis of some, probably of all, 

 (if we were sufficiently acquainted with their nerve anatomy), may 

 be at once declared from the corresponding condition of dorsal chord, 

 as I shall have occasion to shew in the sequel of this paper. 



Thus it appears that insect classification has improved, so far as 



