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



the parasite was attached to its host. In the case of Sylon schneideri, however, I observed 

 that the connection takes place in much the same way as Delage has described it in 

 Sacculina. From a well-developed and rather voluminous basis (the "membrane basilaire" 

 of Delage) numerous roots pass into the interior of the host, and in order to investigate 

 this attachment it is necessary to make transverse sections of the host with the parasite 

 attached to it. A part of the abdomen (the dorsal half having been removed) of a small 

 specimen of Hifpolyte pusiola with the Sylon attached, was embedded in paraffin in the 

 usual way, and sections cut with the aid of the microtome. 



Some of the sections so made are shown in PI. CL. figs. 4-6. As it is not my 

 intention to publish here an elaborate anatomical and histological description of Sylon — 

 since both in regard to quantity and quality the material at my disposal was not sufficient 

 — but only to give a preliminary orientation with regard to these little-known animals, a 

 few words must suffice to describe this basilary membrane. It forms a circular disc equal 

 in area to about one-fifth of the whole surface of the Sylon, and is not very thick, in the 

 preparation shown in PI. CL. fig. 4 measuring only about 0'2 mm.; it is composed of con- 

 nective tissue, the nuclei being very small and numerous. The roots are not very abundant, 

 but rather elongate and much ramified. In one respect there seems to exist an interesting 

 difference between Sylon and Sacculina — in the latter genus the roots penetrate within the 

 body of the Crab until they reach the wall of the intestine, but in Sylon, on the contrary, 

 they as a rule do not reach so far. In Carcinus msenas, at the place where Sacculina is 

 attached, the distance between the basilary membrane and the wall of the intestine is 

 inconsiderable; in Sylon the same membrane is separated from the wall of the intestine 

 by a dense mass of muscles (PL CL. fig. 4, m). Most of the roots (PL CL. figs. 4, 5, r) 

 terminate on the ventral aspect of this mass of muscles, and only one root could be 

 followed running close to the lateral surface of the abdomen of Hippolyte and directed to 

 the dorsal part of the body. Most probably therefore Sylon lives, at least partly, on the 

 blood of its host, and only to a limited extent draws its nourishment from the intestinal 

 contents. Branches of these roots surround the central nervous system, passing through 

 the abdomen in a very curious way (PL CL. figs. 4, 5, «). 



According to Delage the basilar membrane and the roots belong to the internal part 

 of the Rbizocephalid, the external part consisting of the visceral mass and of the mantle. 

 The name "visceral mass" is perhaps not quite exact, as there is no trace of viscera, in 

 the ordinary sense of the word (intestine, &c), the contents being made up almost 

 exclusively of one organ, namely, the very bulky ovary. After soaking in absolute 

 alcohol, the ovary forms a very compact and hard body, which cannot easily be stained, 

 is very brittle, and causes great trouble when cutting sections. It consists of extremely 

 numerous more or less unripe eggs ; in the specimens I investigated almost nothing could 

 be observed of the true ovarian tubes, the ova being closely packed together in almost 

 every direction. The latter are all nearly in the same condition of ripeness ; each con- 



