56 Royal Society, 



external circumstances, or become exhausted by their efforts at effect- 

 ing the growth or modifying the form of different parts. Thus the 

 ganglia and nervous cords undergo great changes both in their form 

 and situation, and also in their number, during the passage of the 

 insect from the larva to the pupa state 3 and after these changes have 

 been carried to a certain extent, they are suspended for several weeks, 

 during which the insect remains in a state of hybernation ; but at the 

 expiration of this period the changes again proceed, and are continued 

 uninterruptedly, till the insect attains its ultimate or perfect stage of 

 development. The Sphinx ligustri remains in the pupa state during 

 at least forty-two or forty-three weeks ; thus affording ample oppor- 

 tunities of examining the whole progress of the changes which take 

 place in the structure of different parts. The concentration of the 

 nervous system, which was commenced in the larva, proceeds to a 

 mucn greater extent while the insect is inclosed in the pupa, and is 

 continued for a short time after it has assumed the imago state. The 

 double origin and connexions of the nerves distributed to the wings 

 are described, and a conjecture offered as to the object of this ar- 

 rangement, which appears designed to establish a harmony of action 

 between the wings, in those insects, especially, which are remarkable 

 for velocity and power of flight j a different disposition being adopted 

 in those which fly with less regularity or speed. The nerves of the 

 organs of sense, as the antennae, eyes, proboscis, and apparatus for 

 manducation, are traced and minutely described, and a comparison 

 instituted between them and the nerves which have similar offices in 

 vertebrated animals. The author traces the origin and course of the 

 nerve corresponding to the pneumo-gastric, or par vagum, and shows 

 that it is distributed chiefly to the organs of digestion and the respi- 

 ratory passages. He next describes the anterior lateral cephalic 

 ganglia, which, from their position, might be regarded as auxiliary 

 brains. The situation and course of .another nervous tract, which 

 from its extensive connexions and peculiar mode of distribution is 

 considered as corresponding to the sympathetic system, are also 

 traced. The author notices a set of nerves which, adopting the views 

 of Sir Charles Bell, he considers as analogous to those which the lat- 

 ter has denominated the respiratory nerves of vertebrated animals ; 

 and among a great number of interesting observations, of which it is 

 impossible to give any abridged account, one of the most remarkable 

 is the discovery that the priniary longitudinal nervous cords of in- 

 sects consist of two tracts, the one situated over the other, corre- 

 sponding to the two columns of which the spinal cord consists in ver- 

 tebrated animals j the one appropriated to sensation, and the other to 

 voluntary motion ; the nerves from each of these tracts being variously 

 combined, according to the purposes they are designed to fulfill. This 

 important distinction, which was first traced in the nervous cords of 

 the Lobster, was afterwards distinctly observed by the author in the 

 Scorpion and the Scolopendra, and lastly, in several species of insects, 

 as the Grijllus viridissimus, the Carabus, the Papilio urticeB, and the 

 Sphinx ligustri. Numerous drawings of the parts described accom- 

 pany the paper. 



