REPORT ON THE HOLOTHURIOIDEA. 87 



on the inner margin of the nave. The dichotomously branched bodies are discoidal and 

 more or less circular ; their appearance will be most easily understood by looking at my 

 figures. The three above-mentioned forms of deposit are found present in more 

 or less abundance even in the pedicels, processes, and tentacles. The end of the 

 pedicels is strengthened by a terminal perforated plate, surrounded by numerous 

 transversely placed spicula (PI. XXXVI. fig. 19), which decrease in number towards the 

 middle of the pedicel, where they cease totally. These spicula are fusiform, rather 

 long and slender, straight or arcuated, with their ends more or less spinose, a few being 

 branched, and others enlarged in the middle and punctured with one or more holes. 

 The dorsal processes have only a few scattered spicula which do not lie crowded together 

 at their tops. Many more or less arcuated spicula of very variable size are present 

 in the tentacles. The deposits of the oral disk are partly made up of wheels of 

 various dimensions and clichotomously branched bodies, partly of simple or branched, 

 straight or slightly curved spinose spicula which have sometimes a cruciform shape. 



The calcareous ring forms a continuous whole of an extremely fragile and spongy 

 structure, which a solution of potass separates into pieces, though not into distinctly regular 

 ones. The posterior part of the ring, or that portion which is directed upwards, when in 

 its proper position, is penetrated by five rather large holes. The polian vesicle is 

 unusually small, only 6 mm. long. The rnadreporic canal (PI. XXXVIII. fig. 6) communi- 

 cates with the exterior by a number of pores, from eight to about fifty, situated close 

 together immediately in front of the genital process, and about 20 mm. behind the anterior 

 extremity of the body. When the number of pores is great, they are closely crowded 

 on a small space, which being slightly depressed below the surface of the surrounding 

 perisoma, becomes strikingly like a rnadreporic plate (PI. XXXVIII. fig. 7). These pores 

 communicate with a corresponding number of minute canals which pierce the perisoma 

 and open into a comparatively thick rnadreporic tube. The above-mentioned canals often 

 bear one or more branches, and their walls contain numerous dark violet pigment cells, 

 thus becoming most conspicuous ; they are often of a flask-shaped form, and completely 

 wanting in calcareous deposits. The rnadreporic canal itself is strengthened by a great 

 number of thread-like, irregularly branched calcareous bodies (PI. XXXVIII. fig. 8) of 

 variable size. The pedicels communicate with ambulacra! cavities, whfle the processes, 

 on the contrary, are in connection with ambulacral vesicles. The spacious ambulacral 

 cavities, which are elongated and lie in the thick layer of connective tissue of the 

 ventral perisoma, are of two kinds according as they belong to the pedicels of the 

 inner or outer row ; those in connection with the pedicels of the outer row are 

 widest where they communicate with the ambulacral vessels, while the other cavities 

 are here comparatively much narrower, but increase in such a manner, that their 

 Greatest width is at a considerable distance from the ambulacral vessels. Both kinds 

 of ambulacral cavities (PI. XLII. fig. 4) terminate in several short csecal prolongations. 



