30 THE SPONGES. 



specimen from this station is fragmentary, but appears to have belonged to 

 a much-flattened sponge similar to the one just described. It is of course 

 possible that in the packing these specimens have been artificially flattened. 

 There is, however, every indication that the present shape is approximately 

 the natural one. 



The parenchymal macroscleres are oxydiacts and oxyhexacts. The 

 oxydiacts are very abundant, scattered in all directions through the par- 

 enchyma, chiefly in tracts, but also singly. They are smooth, with or 

 without a median swelling, the rays tapering evenly to points. The size 

 varies from 500 fx. long by 8 /n, thick, near the middle, to 3 mm. long by 



28 fi, thick. The oxyhexacts are few in number. The rays are 



smooth, straight, and tapering, measuring in a typical case 700 fi long 

 by 48 /x thick at the base. The hypodermalia and hypogastralia are 

 alike, and are smooth oxypentacts and oxydiacts. The oxypentacts are 

 abundant, with no trace of the distal ray, the other rays tapering to 

 points. They vary in size from small ones with tangential rays 150 /x x 

 12 /x to large ones with tangential rays 600 y^t x 48 /x. The proximal 

 ray is in general longer than the tangential rays, but on the gastral sur- 

 face it is sometimes shorter. The diacts are abundant, sharing with 



the tangential rays of the pentacts in forming the supporting reticulum 

 of the surface. They are similar to the diacts of the interior. 



The common and characteristic form of parenchymal microsclere is a 

 micro-oxyhexact with slender, curved, and minutely denticulate rays, 

 30-45 /x long and 2 /x thick at the base (Fig. 9, Plate 1). The denticula- 

 tions are sharp and just perceptible, with a power of 600 diameters. The 

 curvature is well marked. Mingled with these are a good many similar 

 oxyhexacts, in which the ray is either straight (Fig. 8, Plate 1) or shows 

 only a very slight curvature. These average a larger size, the ray length 

 being 40-60 /x. Oxyhexacts and oxypentacts witli straight, minutely den- 

 ticulate rays, 60-80 /x long, are found sparsely in the parenchyma, and 

 in or near the walls of some of the canals. They are probably in all cases 

 canalaria. 



The dermal pinules (Fig. 3, Plate 1) are slender spicules, in which the 

 distal ray ends in a pretty long slender point ("endspitze"), and bears sharp 

 spines, which are not thickly crowded. The lower part of the distal ray, 

 ^ to J the total length, is smooth. The tangential rays are smooth, or 

 nearly so, and pointed. There is no trace of the proximal ray. The distal 



