FORMS OF DEEP-SEA ASCIDIANS. 289 



ventral wall. Only the lateral fibres are indicated in the figure ; they are prolonged 

 superiorly in a horizontal direction along the upper margin of the dorsal wall of the 

 test-cavity. The tubular cavity of the stem is rilled by a core composed of muscular 

 fibres embedded in gelatinous tissue, a prolongation of the mantle. 



Of the gill-sac only a small portion remained intact in situ, but fragments here and 

 there attached indicated an arrangement as shown in the figure. The small portion 

 in situ lay over the nerve-ganglion. The fenestrations in the membrane are small, 

 simple, and irregular (fig. 3) . 



The mouth is situate nearly in the middle line (m, fig. 1). It leads by a short trans- 

 parent oesophagus to a stomach (s), which has opaque walls corrugated externally; and 

 this viscus leads into a rectum which curves up to end at the exhalant aperture. 



Beneath the stomach is a tubular heart with a wide vessel leading from it downwards 

 towards the stem. 



In the loop formed by the oesophagus, stomach, and rectum is the large ovisac or 

 ovary, which is circular in outline. The elongate tubular testis running parallel to the 

 rectum in the middle line terminates posteriorly internally to the ovisac, its lower end 

 spreading out into a series of ramifications, which appear very like large nerve-fibres. 

 The testis-tube opens into the exhalant aperture close to the rectum, as does also the 

 oviduct, which lies to the dorsal side of the testis-tube and in the same bine with it. 



The ovisac was full of very large ova, measuring as much as 1/5 millim. in diameter 

 (fig. 5). These ova, on slight pressure being appKed, were discharged from the oviduct. 

 They were found to consist of a very thick transparent test, with contents composed of 

 oily yelk-globules, without a germinal vesicle. 



The testis was tumid, and full of an opaque white matter, which was discharged on 

 pressure in tenacious threads composed of spermatozoa. 



The spermatozoa are very small. They were examined under a Hartnack No, 10 

 (immersion system). They consist of an elongate rod-like head, measuring '005 millim. 

 in length, and an excessively fine tail, the length of which could not be determined. 

 All the spermatozoa examined had a small transparent vesicle attached to one side of 

 their heads, as shown in the figures (fig. 6). 



This Ascidian appears to be allied to Boltenia ; but it is especially remarkable because 

 of the occurrence in its test of symmetrically arranged cartilaginous plates, which form 

 a pattern. The name Hypobythius caly codes is proposed for it. 



II. Octacnemtjs BYTHius, gen. et spec. nov. (Plate XLIV. figs. 7-13.) 

 This stellate Ascidian was trawled March 1st, 1875, in 1070 fathoms, lat. 2° 33' S., long. 

 14-1° 04' E., about 40 miles north of Rossy Island, Schouten Islands. Erom its peculiar 

 appearance, due to the presence of the eight long radiating conical processes of the test, 

 the animal was at first supposed to be a Medusa. The single specimen was considerably 

 injured, the muscular networks maintaining their attachments in only three of the conical 

 processes, but the test was entire. 



The test of the animal is gelatinous and hyaline. On the under surface the body 

 presents a flat area of a nearly oval form (fig. 7). The border of this base is thickened 



2 Q 2 



