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



I'ouud exhalcut orifice of the effereut canal system which lies underneath every outwardly 

 arched elevation of the walls of the tube {PI. V. fig. 12 ; PI. VI. fig. 3). On the projecting 

 ledges there are also numerous smaller furrows, and the orifices of shorter efi'erent canals. 

 Although the preservation of tlie soft parts of the specimens handed over to me for 

 examination is not so good as that of many specimens of Eujilectella aspergillum, I 

 have still succeeded in definitely determining the essential structural relations. 



The much folded layer of saccular chambers is, as in Ewplectella aspergillum, united 

 with the external skin by means of the outer trabecular framework, and with the gastral 

 membrane by means of the similar internal trabeculte. In this also, the latter is con- 

 tinued into the terminal diverticula of the efferent passages, forming a continuous 

 internal lining (PI. VI. fig. 3). 



The thickness of the tube-wall amounts, in the arched portions, to about 3 mm., and 

 through the inwardly projecting ledges to between 3 '5 and 4 mm. 



The chief skeletal framework is formed of strong pentacts, in which the four cruciately 

 disposed rays, which vary from 1 to 3 cm. in length, are arranged longitudinally and 

 circularly so that they are closely apposed to each other longitudinally, or even cross one 

 another transversely, and so that the longitudinal rays always lie externally to the 

 circular. The breadth of the quadrate meshes thus formed amounts to 3 or 4 mm. The 

 radial unpaired ray, which projects freely outwards in a straight or slightly curved course, 

 attains a length of 1 '5 to 2 cm., and, like the four other rays, runs out to a simple point. 

 A radial ray does not, however, arise from every point of intersection of the longitudinal 

 and circular fibrous strands ; on the contrary, both in the longitudinal and transverse 

 directions, a simple point of intersection without an independent pentact always alternates 

 with one which is occupied by the intersecting nodes and the radial rays of a pentact 

 (PI. V. fig. 15). 



The intersections of these longitudinal and transverse fibres correspond, not to the 

 middle of an elevation lying between four parietal apertures, but to those external 

 furrows which unite the parietal apertures in spiral lines (PI. V. figs. 1, 12). 



The longitudinal, as well as the circular rays of the large pentacts, are closely 

 surrounded by a mantle of delicate comitalia, whose greatly prolonged rays apply 

 themselves either parallel to, or in gentle windings round the thick round pentact-rays. 

 As a rule the comitalia consist of triacts, wdiose unpaired ray stands at right angles to 

 the two long rays which lie in one line, and serves for the support of the adjacent soft 

 parenchyma. Long diacts with central intersecting nodes are also frequent (PI. V. 

 fig. 14). The extreme ends of these comitalia form blunt points, and exhibit a slight 

 roughness, while the rest of the ray is smooth. With the comitalia are associated those 

 numerous parenchymalia, with from two to six shghtly bent or straight rays (PI. V. 

 figs. 16-20), which serve for the support of the parenchyma of the soft parts between the 

 principal strands of fibres. They are somewhat thicker than the comitalia, and their 



