NERVOUS SYSTEM. 89 



several arising from its under surface ; in outline, however, 

 it may be said to be divided into a posterior and anterior 

 half; the latter being somewhat heart-shaped, and the 

 posterior half elongated. The nerves going to the five 

 posterior pairs of cirri rise from the posterior margin of the 

 ganglion, and run for some distance in a sheet, parallel and 

 close together ; the pair, however, going to the second pair 

 of cirri soon branches off from the others. Each of these 

 nerves enters at the inner and posterior margin of the cirrus 

 to which it belongs, and, at least in the case of the first pair, 

 divides into two branches as it enters. The nerves (PL 27, 

 fig. 1, f5, r 6) going to the fifth and sixth pairs of cirri are 

 more closely united together than are the others, and 

 appear, till they branch off, like a single large nerve. That 

 which belongs to the sixth cirrus gives off, opposite to the 

 fifth cirrus, a branch (s) nearly as large as itself, which enters 

 the probosciformed penis. I may remark, that homologi- 

 cally this is the only abdominal nerve in any cirripede of 

 the Order. From the under side of the nerves which run 

 to the five posterior pairs of cirri, small branches are given 

 off, extending dorsally into the thorax. 



The anterior end of the great infra-cesophageal ganglion 

 is formed by the union of a set of nerves, extending parallel 

 in a bundle in a directly opposite direction to those running 

 to the five posterior pairs of cirri. These nerves consist of an 

 outer larger pair (r l) entering the first pair of cirri ; and 

 within these, and rather dorsally to their roots, we have the 

 circa-cesophageal chord (c, c), or collar nerve; between the 

 roots of the latter, and on the ventral surface (or near side 

 of the figure), there are three closely united, small pairs, 

 running to the gnathites, and, as I believe, to the olfactory 

 sacks. From the under (or dorsal) surface of the anterior 

 end of the ganglion, two nerves, larger even than the circa- 

 cesophageal chord, and which I shall call the splanchnic pair 

 {d, d) arise ; and the singular course of these nerves will pre- 

 sently be described; between this great pair, there is a 

 single (b) medial nerve, which runs down and branches into 

 that large diverging muscle, which is attached to the upper 

 ventral surface of the stomach. Posteriorly to these three 

 nerves, we have two pairs of much smaller nerves (not 



