ORGANIZATION OF CEKATOCEl'IIAI.E OSAWAI. 



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of which the third (the parapodial nerve) is the strongest while all the rest 

 are about equally slender nerves. The first or the anteriormost pair is 

 the nerve that goes to the intersegmental partition (fig 8, int.). The 

 next following, i. e., the second, pair supplies the oblique muscles, and the 

 fourth or the last pair the ventral longitudinal muscle. The third pair, in 

 front of the last, is the parapodial nerve. It traverses laterad between 

 the ventral longitudinal and the circular muscles. Reaching the base of 

 the ventral cirrus, it forms a small ganglion, the parapodial ganglion (fig. 1, 

 pd,g.). This sends out laterally two nerves. One of these supplies the 

 ventral cirrus (v. c.) as well as the distal parts of the parapodium ; the other 

 ascends along the posterior wall of the parapodium to the base of the dorsal 

 cirrus. Here it again forms a small swelling, whence arise two small 

 branches ; one of these proceeds into the dorsal cirrus and the ligula, 

 while the other supplies the dorsal parts of the segment and the dorsal 

 longitudinal muscle. 



The ventral nerve-cord is of the usual shape and structure Cross- 

 sections (fig. 11.) show that it is longitudinally traversed by two, rather 

 wide, neural tubes throughout the entire length, and further that it runs in 

 a deeper position than the hypodermis, from which it is separated by a 

 space occupied by muscular tissues. 



With regard to the proboscidial nervous system, much difficulty was 

 experienced in making out the arrangement of the nerves on account of 

 the hard jaws which seriously interfere with the cutting into serial sections. 

 However, I have succeeded in clearing up the following points with reference 

 to the nerves of the proboscis in the fully protruded state 



Altogether four pairs of nerves are given off from the brain and the 

 oesophageal ring into the proboscis (fig. 8 ) : 2 pairs from the brain (viz r 

 the I. and the VII. cerebral nerves), 1 pair from the anterior cirrus ganglia 

 and I pair from the anterior side of the cesophagial connectives about mid- 

 way between the anterior cirrus ganglion and the infra-œsophageal ganglion. 

 Since the I. cerebral nerves split each into two soon after leaving the brain, 

 there are in all ten nerves that enter from behind into the outer wall of the 

 protruded proboscis. About half-way to the tip of the latter, all the ten 



