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



they are disposed in a simple row or in a double crown, though I believe the former to 

 be the case. The end of the tentacles carries five or six processes, of which a couple 

 appear to be larger than the others. 



The perisoma is hard, unpliable, and particularly thick, the latter is especially the 

 case with the body- wall along both sides on the transition between the ventral and dorsal 

 surface where the layer of connective tissue is greatly developed. Three different layers of 

 calcareous deposits are distinguishable. The outermost layer consists of scattered, very 

 small, more or less curved, and branched spicula (PL XXXI. fig. 8) of various shapes. The 

 intermediate layer is composed of closely placed plates (PL XXXI. figs. 4, 5, and 6), which 

 cover one another completely or with their edges alone, and give the perisoma its firmness. 

 These plates are partly large, about 7 mm. in diameter, and of a more circular form, partly 

 smaller arranged round the former and of a more variable shape. Each plate presents 

 the appearance of a flat network with the upper surface convex, its greatest thickness being 

 at its centre ; its under surface is perforated by numerous more regularly rounded holes, 

 while the upper one presents an irregular network provided with some small scattered 

 spines. The innermost layer is made up partly of more or less branched spicula and 

 partly of larger net-like bodies (PL XXXI. fig. 9) with wide meshes. Besides those 

 deposits I have found some minute bodies in the form of grains, which are some- 

 times joined together in bands within the connective tissue, but those are probably a 

 chemical product formed during preservation in alcohol. The tentacles contain a 

 minute number of deposits in the form of small scattered spicula. The deposits of the 

 pedicels and processes strongly resemble the above-described plates, though smaller ; 

 the ends of the pedicels have no supporting terminal plate, but are instead provided 

 with small generally more or less branched spicula (PL XXXI. fig. 7). 



From want of material I have not been able to closely examine the calcareous 

 ring, but it appears to resemble in form as well as in structure that of Deima fastosum ; 

 it is extremely fragile, and becomes separated into small pieces on being treated with 

 solution of potass. The polian vesicle reaches a length of 30 mm. The water-vascular 

 system corresponds with that in Oneirophanta, and in regard to its details I refer to 

 the anatomical part of the report. The cloaca is insignificant. The digestive tract is 

 attached to the inside of the dorsal perisoma by a mesenteric membrane. The repro- 

 ductive organ (PL XLVI. fig. 5) consists of two fascicles, one on each side of the rnedio- 

 dorsal mesentery, each fascicle composed of from five to six long, narrow cylindrical tubes, 

 which carry a number of larger or smaller globular csecal sacks. A great part of the 

 internal organs such as the water-vascular system, the pseudhaernal vessels, the ali- 

 mentary canal and the genital organs, contain a great abundance of calcareous deposits in 

 their walls, which generally have the form of branched or simple more or less curved 

 spicula, of net-like bodies and of perforated plates. The mesentery also contains 

 numerous small spicula. 



