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



and between these two an immense series of gradations exists. The short and arcuate 

 spokes — in the large wheels from eight to ten in number, or sometimes less, while the 

 smaller wheels have twelve or thirteen — support a large, discoidal nave with a large 

 hole iu its middle, from the edge of which proceed five, sometimes four or six, small 

 slightly arcuate rods, which converge to form a conical figure, the top of which is 

 directed towards the inside of the body-wall. The wheels are concave, more or less like 

 a crown, and have their felly directed outwards from the body. The ventral perisoma is 

 almost exclusively strengthened by small wheels which are usually rather scattered, 

 whereas wheels of all dimensions are to be seen on the dorsal surface ; nowhere are these 

 deposits so crowded as in the tentacles and processes. The wheels lie in the outer layer 

 of the connective tissue, while the spicula are placed close to the layer of circular 

 muscular fibres. Besides those above-mentioned deposits I have found here and there, 

 though especially in the processes, some minute, round bright particles, and numerous 

 slightly larger bodies of a discoidal form ; these are doubtless chemical products which 

 have originated by preservation in alcohol. The layer of connective tissue of the in- 

 tegument contains an immeuse quantity of violet pigment which is partly scattered, 

 partly crowded in masses, and partly disposed in lines which cross one another in all 

 directions, thus forming an obvious network ; the large nerve-cords as well as their 

 ramifications contain pigment, and the pigmented network just mentioned is constituted 

 by them. 



The sole-like terminal part of the pedicels is strengthened either by a single, large, 

 more or less circular perforated plate (PI. XXXIV. fig 1), with the holes in the centre 

 considerably larger than at the circumference, or by some smaller ones ; round these 

 plates He partly some short, thick spicula of a variable shape, which are often provided 

 with branches, and have their slightly enlarged ends spinose, and partly longer arcuated 

 unbranched ones. The processes contain, besides a multitude of wheels of various 

 dimensions, some scattered spicula. The ends of the tentacles are supported by a great 

 number of unbranched spicula of diverse forms and dimensions resembling those of the 

 pedicels ; the stem of the tentacles, however, contains only a few scattered spicula but 

 a greater number of wheels. 



The calcareous ring (PL XXXVII. fig. 11) seems to be made up of a continuous 

 spongy, extremely fragUe and thin network, no radial and interradial pieces being 

 distinguishable. By treating it with a solution of potass it separates into small pieces or 

 fragments. The very pliable ring is capable of being considerably contracted, thus form- 

 ing numerous larger or smaller wrinkles. The polian vesicle, 20 mm. long, has a con- 

 siderable width. The ambulacral cavities (PI. XLII. fig. 7) are small, and do not give 

 off any branches ; their form is more or less evidently triangular, or approaches almost 

 the shape of a semicn-cle. The madreporic canal (PI. XLIII. fig. 4a) presents the 

 greatest difference when compared with that of Oneirophanta; it runs out, as usual, from the 



