876 



GENERAL STRUCTURE AND FUNCTIONS 



Fig. 125. 



that of the entire body. (Fig. 124.) There is a small ganglion (i) 

 situated anteriorly, which sends nerves to the commencement of the 

 digestive apparatus, and is regarded as the oesophageal or digestive 

 ganglion. Immediately behind it is a larger one (a) called the 

 cephalic or cerebral ganglion, which sends nerves to the organs of 

 special sense, and which is regarded as the seat of volition and 

 general sensation for the entire body. Following this is a pair of 

 ganglia (3, 3), the pedal or locomotory ganglia, which supply the 

 muscular mantle and its foot-like expansion, and which regulate 

 the movement of these organs. Finally, another ganglion (4), situ- 

 ated at the posterior part of the body, sends nerves to the branchiae 

 or gills, and is termed the branchial or respiratory ganglion. All 

 these nervous centres are connected by commissures with the central 

 or cerebral ganglion, and may therefore act either independently 

 or in association with each other, by means of these connecting fibres. 

 In the third type of animals, again, viz., the articulata, the gene- 

 ral plan of structure of the body is different from 

 the foregoing, and the nervous system is accord- 

 ingly modified to correspond with it. In these 

 animals, the body is composed of a number of 

 rings or sections, which are articulated with each 

 other in linear series. A very good example of 

 this type may be found in the common centipede, 

 or scokpendra. Here the body is composed of 

 twenty -two successive and nearly similar articu- 

 lations, each of which has a pair of legs attached, 

 and contains a portion of the glandular, respira- 

 tory, digestive and reproductive apparatuses. 

 The animal, therefore, consists of a repetition of 

 similar compound parts, arranged in a longitudi- 

 nal chain or series. The only exceptions to this 

 similarity are 1 in the first and last articulations. 

 The first is large, and contains the mouth ; the 

 last is small, and contains the anus. The first 

 articulation, which is called the "head," is also 

 furnished with eyes, with antennae, and with a 

 pair of jaws, or mandibles. 



The nervous system of the centipede (Fig. 125), 

 corresponding in structure with the above plan, 

 consists of a linear series of nearly equal and similar ganglia arranged 

 in pairs, situated upon the median line, along the ventral surface of 



NKRVOPS SYSTEM 

 OF CENTIPEDE. 



