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



the lumen of the tube, and constricting it like a diaphragm. This doubtless serves to 

 close the tube, since it is covered by a marked layer of muscle fibres, running circularly 

 round the opening. 



Where no stomidium is placed, the oral disc exhibits on its ectodermal side a 

 thick layer of radial muscle fibres, arranged in simple lamella?, which, at most, branch 

 but once. The lamellae being higher midway between two mesenteries than elsewhere, 

 the radial ridge-like thickenings of the oral disc are the result. 



With reference to the relations between the stomidia and the inter- and intra- 

 mesenterial chambers, in my former publication I expressed the opinion that an 

 intra-mesenterial chamber might carry more than one stomidium, Liponema thus 

 approximating to the Corallimorphidae ; an opinion which I can now designate as 

 erroneous, on the ground of more accurate investigation. Each intra-mesenterial 

 chamber possesses but one stomidium, which is the more closely approximated to the 

 centre of the oral disc, in proportion as its adjacent septa are of older formation. 



The stomatodseum is brownish-violet in tint, and 2 cm. long ; on it are placed 

 the marked siphonoglyphes, about 1*5 cm. in breadth, projecting considerably at the 

 lower part of the tube, where they pass into the boat-shaped stomatodseal cone. They 

 are bounded by two stout, transversely pleated, lips. Further, the stomatodaaum is 

 marked by about 200 longitudinal folds, of which some 80, by their stronger build, 

 deserve the name of primary folds. Between every two primary folds lie, in many 

 cases, two secondary folds ; but at some places one only may occur, or they may be 

 entirely wanting. 



The number of mesenteries was determined by the method before mentioned, that of 

 cutting out a sextant of the animal and studying it closely anatomically. I found six 

 cycles, in all therefore 192 pairs of mesenteries. In the first four cycles all the. 

 mesenteries reach the stomatodseum, though those of the first two cycles only are 

 attached to it for its whole length ; they all possess wide openings near the edge of 

 the lip (internal mesenterial stomata), and their muscular nature so far preponderates 

 that only those of the fourth cycle carry generative organs. In this respect these 

 mesenteries of the fourth cycle agree with those of the fifth and sixth, but the muscular 

 development of the latter is considerably inferior to that of the others. The mesenteries 

 of the sixth cycle are practically nothing else than small genital folds, projecting but 

 slightly into the ccelenteron, and never provided with mesenterial filaments. 



Of the generative organs I found exclusively the testicular follicles, containing 

 spermatozoa in parts ripe, in parts only commencing to develop. 



It is possible that in this animal a further growth takes place, with the formation 

 of new mesenteries ; this I infer from the great number of stomidia. In the sextant 

 investigated they amounted to about 120, or to 700-800 for the whole animal. Since 

 only about 196 intra- and inter-mesenterial chambers are present, and each of the 



