COMPARATIVE ANATOMY AND PHYSIOLOGY. 



113 



148. Hitherto we have spoken only of that division of the nervous system 

 of the Articulata, which may be regarded as corresponding with the sensory 

 and locomotive ganglia of the Mollusca ; namely, the cephalic, the pedal, and 

 (in some instances) the palleal. We have next to inquire what we find corre- 

 sponding with the branchial ganglion. It is to be recollected that the respira- 

 tory apparatus of Insects is diffused throughout the whole body, so that its 

 presiding system of nerves must be proportionally extended ; and we are, 

 therefore, prepared to find the branchial ganglion of the Mollusca repeated, 

 like the pedal, in each segment. Besides the nervous trunks proceeding from 

 the ventral cord at its ganglionic enlargement, we find, in most of the Articu- 

 lated classes, a series of smaller nerves, given off at intermediate points, with- 

 out any apparent swelling at the points of divergence. The connections of 

 these are most distinctly seen in the thoracic region, just as the Larva is pass- 

 ing into the Pupa state ; for the cords of the ventral column then diverge, so 

 that an additional tract may be seen, which occupies the central line. By a 

 close scrutiny, this tract may be found in the perfect Insect, on the superior or 

 visceral aspect of the cord ; and its nerves are given off from minute gangli- 

 onic enlargements upon it. It seems to be quite unconnected along its whole 

 course with the column upon which it lies. Its nerves, however, communi- 

 cate with those of the sensori-motor system ; but they have a separate distri- 

 bution, being transmitted especially to the trachea, on the parietes of which 



Fig. 13. 



Parts of Nervous System of Articulata, after Newport. A, single ganglion of Centipede, much enlarged, 

 showing the distinctness of the purely fibrous tract, fc, from the ganglionic column, a. B, portion of the 

 double cord from thorax of Pupa of Sphinx ligustri, showing the respiratory ganglia and nerves between 

 the separated cords of the symmetrical system, c, view of two systems combined, showing their arrange- 

 ment in the Larva; a, ganglion of ventral column; 6, fibrous tract passing over it; cc, respiratory system 

 of nerves distinct from both. 



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