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



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

 towards the stem (PI. XXXVII. fig. 1, /;,). 



" In the loop formed by the cesojihagus, 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 exhalent aperture close to the rectum, as does also the oviduct, w r hich lies 

 to the dorsal side of the testis-tube and in the same line with it. 



" The ovisac w r as full of very large ova,measuring as much as 1'5 millimetres in diameter. 

 These ova, on slight pressure being applied, 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 opacpue wdnte 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 milli- 

 metres 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 (PI. XXXVII. fig. 5)." 



The above comprises almost the whole of Professor Moseley's description of this 

 remarkable form, and I have only a few remarks to add. Mr. Moseley supposed that it 

 was allied to Boltenia. The peduncle, however, is deceptive, and does not indicate any 

 relationship to the Bolteninae. The whole organisation, and especially the structure of 

 the branchial sac, taken along with the fact that, as far as is known, reproduction is not 

 performed by gemmation, shows that Hypobythius must be referred to the Ascidiidae, 

 among which we have already a new deep-sea pedunculated genus, Corynascidia. 



The body form in Hypobythius calycodes is vase-shaped, with a moderately long 

 peduncle attached to the narrow posterior end, whde the anterior end is broad and 

 truncated. The atrial aperture is placed on the dorsal edge near the anterior end, while 

 the branchial aperture is indistinguishable, and must have been on the torn anterior end, 

 but probably of much smaller size than is represented by Mr. Moseley in his restoration 

 (PI. XXXVII. fig. 1). 



The test is cartilaginous and thin, except in certain localities, where denser carti- 

 laginous thickenings or nodules are developed symmetrically, as seen in Plate XXXVII. 

 figures 1 and 2. They are especially developed along the dorsal edge, outside the 

 viscera, and it wdl be seen that in this locality in Hypobythius moseleyi also the test is 

 somewdiat strengthened. 



The mantle is thin and membranous, and has a feeble but distinct musculature. 

 The muscle bands are very fine but numerous. They run longitudinally, and are chiefly 



