RHABDOCALYPTUS CAPILLATUS. 281 



The roundish entrances into the incnrrent canals are on the 

 wliole rather wide. In large specimens they may attain 4 or 5 

 mm. in diameter, those of nearly similar sizes being separated 

 from one another by an interspace measuring in width nearly as 

 much as their own diameter. 



The entire inner surface of the wall is covered by a gastral 

 lace work with regularly quadrate meshes of 180-240 /^- (on the 

 average 175 /-«) on a side. When viewed in an oblique direction 

 under the hand-lens, the gastral layer presents a velvety appearance 

 on account of the projecting proximal rays of the hexactinic 

 gastralia. Directly beneath it are distinctly observable hypogastral 

 strands of varying strength. They run in various directions and 

 by intersecting form wide and irregularly shaped meshes. As 

 usual they are frequently seen to stretch right across the excurrent 

 canalar apertui'es. The stronger strands may push out the gastral 

 surface in a ridge-like line. 



A somewhat different state of the gastral surfece obtains 

 in very small young specimens. Until these have grown to 

 a certain size, the gastralia are not present in numbers suffi- 

 cient to form a continuous layer. Hence, there occur between 

 them gaps by which the excurrent canals open directly and 

 freely into the gastral cavity. The little specimen of PI. 

 XXII., fig. o, still exhibits this condition of the gastral sur- 

 face ; whereas, that of fig. 4 is already in possession of a con- 

 tinuous gastral layer covering the apertures of all the excurrent 

 canals. 



These, in large specimens, are smaller than the average 

 incur rent apertures on the external side, generally measuring 2-3 

 mm. in diameter. They are closely packed together. 



The main canals, both incurrent and excurrent, are pit-like 



