NERVOUS SYSTEM. 



295 



iAJ- 



more elaborate in performing the same operation in the 

 caterpillar of the goat-moth. More recently Strauss-Durck- 

 heim, L. Dufom*, and Burmeister, and especially, with 

 reference to its gradational modification at various periods, 

 M. Herold in the white butterfly, and our own countryman, 

 Ne^A^jort, in the Privet Sphinx, have laboured assiduously in 

 the same field. 



In insects, as in the other articulated animals, this system 

 is quite unhke that of the higher animals, and consists of 

 two medullary cords or threads, exhibiting a series of knots 

 or ganghons, whereby they are united together at certain 

 distances, occuppng the lower surface of the internal part 

 of the body, and being defended from the action of the tho- 

 racic sternums by the internal Y-like processes above de- 

 scribed, as the pro-, meso-, and metathoracic furcse. Some- 

 w times the two gangha of each segment are 



more or less distinct, and sometimes they 

 are united together side by side, occupying 

 the medial line of the body ; and the same 

 occasionally occurs vAi\\ the communicating 

 threads themselves. The nervous ganglia or 

 knots are placed at more or less equal dis- 

 tances from each other throughout the entire 

 length of the insect, sometimes, indeed, so 

 close, that they constitute but two or more 

 gangha. This is the case in the perfect state 

 of the hemipterous insect, Ranatra linearis, 

 for a figure of which I am personally in- 

 debted to John Anderson, Esq., of Richmond, 

 by whom a most elaborate series of prepara- 

 tions of the nervous system throughout the 

 entire range of the animal kingdom has been 

 made, in illustration of a very valuable paper 

 recently published by him with reference to the remarkable 

 analogies exhibited by the human embryo in the various 



// 



Nervous system of 

 Ranatra liuearis. 



