460 PEOF. A. DENDT ON SOME POINTS IN" 



found no sucli connection, but found tlie muscle-tubules or 

 cylinders directly continuous witb tbe transverse muscles of the 

 body-wall. He suggests, however, that they may be rudimentary 

 ambulacral vessels, tbe central ends of whicb have lost their 

 . primitive connection with the radial canal and bave secondarily 

 become united to the transverse muscles of the body-wall. He 

 inclines towards this view on account of the arrangement of the 

 fibres in a bollow cylinder, but this hypothesis appears to be 

 now completely negatived by the discovery of a similar tubular 

 structure in the radiating muscles which connect the cloaca with 

 the body-wall in Gaudina coriacea. 



The radiating bands of muscle to a large extent obliterate the 

 body-cavity in the tail-region, but a portion of the coelom remains 

 conspicuous as a distinct canal (figs. 7, 8, c.c.) surrounding 

 the inner aspect of each of the five radially-placed longitudinal 

 muscles. These longitudinal muscles (r.m.), as usual, form a very 

 conspicuous feature in transverse sections. Each is composed 

 for the greater part of its length of two almost separate halves 

 running side by side, separated from one another by a deep 

 fissure continued outwards from the coelomic canal (fig. 7, c.c.) just 

 mentioned. The surface of the longitudinal muscle is covered 

 by a distinct layer of epithelium which exhibits a very marked 

 thickening on its inner aspect, as shown in fig. 7. This thicken- 

 ing may be due to the contraction of the muscle having thrown 

 the epithelium into folds, but if so, it is difficult to account for 

 its occurrence on the inner aspect of the muscle only. I am 

 inclined to think, however, that it is more likely the expression 

 of a mass of proliferating epithelial cells from which the very 

 numerous corpuscles of the coelomic fluid may be derived. Fig. 7 

 shows four of these corpuscles (corp.) in the coelomic canal at the 

 side of the longitudinal muscle. I have already described them 

 in some detail in my " Observations on the Holothurians of 

 New Zealand." * 



Immediately on the outside of the longitudinal muscle-band 

 lies the radial ambulacral canal or vessel (figs. 7-9, r.a.), lined 

 by distinct epithelium, and with a layer of longitudinal muscle- 

 fibres on its outer aspect. Outside this lies the radial blood-sinus 

 or lacuna, which is extremely small and ill-defined, often not 

 recognizable as a distinct cavity, but shown pretty clearly in 

 some sections (figs. 8, 9, r.s.). Outside this again lies the radial 



* Page 31. 



