No. i.] THE METAMERISM OF NEPHELIS. 37 



The central system lies in the ventral blood sinus underneath 

 the alimentary canal. It consists of a " brain," or supraoesophag- 

 eal part, together with a fused mass of ganglia, the suboeso- 

 phageal ganglia, a chain of 18 ganglia (neuromeres), and a fused 

 mass of ganglia, the anal ganglia. The neuromeres are joined 

 together by paired connectives, and between the connectives 

 lies a small bundle of nerve fibers known as the median nerve, 

 or Faivre's nerve. Within each pair of connectives lie two 

 " colossal " cells. 



The general shape of a body neuromere is a flattened ellip- 

 soid with a slight axial groove. The bodies of the neurons lie 

 in six capsules, arranged about the body of the ganglion in 

 pairs as follows : one pair on the ventral side and one pair on 

 each lateral face. Within the ganglion are two " colossal " 

 cells similar to those in the connectives. Two pairs of nerves 

 arise from the ganglion and divide so as to innervate the somite, 

 as will be described. The anterior pair arises from two roots 

 which quickly fuse, and hence this pair is the homologue of the 

 first two pairs of the three pairs of nerves in Clepsine. Just 

 outside of the ganglion, between the two pairs of nerves, lie 

 two "colossal" cells, one on each side, the prolongations of 

 which fuse into the nerve trunks. These have been called 

 " Leydig's cells." 



Every factor that enters into a body neuromere is found in 

 every neuromere in the central system. 



The anterior nerve innervates the fourth and fifth annuli of 

 the preceding metamere and part of the first annulus of its 

 own metamere. The posterior nerve innervates the few dorsal 

 sensillae of the preceding fourth and fifth annuli, the principal 

 dorsal sensillae of the first annulus, and the lesser dorsal sen- 

 sillae in the second and third annuli. Comparison with Whit- 

 man's description of Clepsine shows this distribution to be 

 identical with that found by him. 



Applying the above plan to the terminal fused parts of 

 the nerve chain, -- the "brain" and suboesophageal ganglia 

 in the head region and the anal ganglia in the posterior 

 end of the body, we have been able to analyse them 

 completely. 



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