NERVOUS SYSTEM OF INSECTS. 491 



in correspondence with the growth of the organs of 

 sense. The next remarkable change is that taking 

 place in the hinder portions of the nervous cords, 

 which are shortened ; at the same time that their 

 ganglia are collected into larger masses, preparatory 

 to the growth of the tail and hinder feet ; so that 

 throughout the whole extent of the system the 

 number of ganglia diminishes in the progress of 

 developement, while their size is augmented. 



All Insects have the nervous system constructed 

 on the same general model as in the last mentioned 

 classes ; and it assumes, as in the Crustacea, various 

 degrees of concentration in the different stages of 

 developement. As an example we may take the 

 nervous system of the Sphinx Ugiistri, of which re- 

 presentations are given in the larva, pupa, and 

 imago states, wholly detached from the body, and 

 of their natural size, in Figures 442, 443, 444.* 



* These figures were drawn by Mr. Newport, from original pre- 

 parations made by himself. The same numbers in each refer to the 

 same parts ; so that by comparing the figures with one another, a 

 judgment may be formed of the changes of size and situation which 

 occur in the progress of the principal transformations of the insect. 

 Numbers 1 to 11 indicate the series of ganglia which are situated 

 along the under side of the body, and beneath the alimentary canal. 

 Of these the first five are the thoracic, and the last six the abdominal 

 ganglia; while the cephalic, or cerebral ganglion (17) is situated 

 above the oesophagus and dorsal vessel, and communicates by two 

 nervous cords with the first of the series, or sub-oesophageal ganglion 

 (1), which is, in every stage of the insect, contained within the head, 

 and distributes nerves to the parts about the mouth. The next 

 ganglion (2) becomes obliterated at a late period of the change from 

 the pupa to the imago state : the third (3) remains, but the two next 

 (4, 5) coalesce to form, in the imago, the large thoracic ganglion ; 

 while the two which follow (6 and 7), become wholly obliterated 

 before the insect attains the imago state, the intervening cords be- 

 coming shorter, and being, with the nerves they send out, carried 



