926 THE VOYAGE OF H.M.S. CHALLENGER. 



the female genital apparatus is to be sought here ; in that case the tubular gland ought 

 to have its opening in the neighbourhood of this invagination also. 



Only in one of the specimens of Sylon schneideri did I observe anything that could 

 be considered to be a testis, and this structure formed an oval compact gland, in connec- 

 tion at one extremity with the wall of the visceral mass, the other extremity lying free 

 between the ovarian cseca. The organ which M. Sars observed and regarded as a- testis 

 is probably the same. In one respect, however, I do not agree with him, for he believes 

 that he observed a small pore at the surface of the mantle, and considers it to be the 

 male genital pore, while I, on the contrary, believe that the testis communicates by means 

 of an opening with the mantle cavity. In PL CL. figs. 5, 6, sections of the testis are 

 represented, figs. 4, 5, and 6 being from the same series ; the preparations follow one 

 another in sequence, from behind forwards, but numerous sections between them are not 

 figured. Continuing the series of preparations in the same direction, soon after the one 

 figured in fig. 6, one follows in which the openings of the mantle cavity are visible. 



The nervous system was observed in Sylon schneideri. The only part of it which 1 

 found was an almost spherical body, composed of small cells with distinct and well- 

 stained nuclei, and situated at the surface of the visceral mass, enclosed in a mass of 

 connective tissue (PL CL. fig. 2, n). Its diameter is about 0"08 mm. In all the sections 

 passing through it there is represented a clear central mass, probably consisting of 

 granular substance, which is characteristic of the nerve-centres of the Arthropoda. In 

 fig. 3 a part of another section, not far in front of that shown in fig. 2, and belonging to 

 the same series, is represented. Here the connective tissue surrounding the nerve centre 

 in fig. 2 is seen to be still more distinctly developed, and encloses a mass of granular 

 substance, which in fig. 2 is just beginning to appear (figs. 2, 3, I). I do not know 

 its nature ; probably it is blood-serum. 



The structure of the Ehizocephalida, so far as regards Sacculina, is now well known. 

 Of Peltogaster our knowledge is rather insufficient ; of Clistosaccus and Sylon almost 

 nothing was known hitherto, and though for the latter genus at least some information is 

 given in this note, much more data are wanted before it will be possible to discuss the 

 affinities, not only of Sacculina and Peltogaster, but of all the members of the interesting 

 family Rhizoeephalida. 



