THE SPONGES. 



21 





The micro-oxyhexacts are 



extremely abundant throughout the 



par 



enchyma. The rays are straight (Plate 3, Fig. 



3) 



or slightly curved 



(Plate 3, Fig. 1), taper gradually to a fine point, and are beset with very 

 minute sharp prickles. The ray is 50-60 /x long, and 4 /x thick at the base. 

 Both the straight and curved varieties are common, although the form 

 with straight rays predominates. 



The dermal and gastral pinuli are alike. They are large, strong pen- 

 tact pinuli (Plate 3, Fig. 4), with no trace of the proximal ray. The 

 distal ray is 320-440 jlc long, with a greatest diameter of 30-60 /x, and a 

 basal diameter of 10-16 /x. The stouter forms, in which the distal ray 

 has a distinctly fusiform outline, as in the figure, are the typical spicules, 

 although slenderer forms in which the distal ray is nearly cylindrical occur. 

 The ray ends above in a terminal cone, and the upwardly projecting scales 

 are narrow and sharp. These degenerate in the lower third of the ray 

 to prickles, below which the ray is smooth. The scales in the thickest 

 part of the ray have a length, measured along their upper border, of about 

 16 /x. The tangential rays are 40-50 /x long and 8-12 /x thick; about 

 cylindrical and then suddenly curving to the point; with a few scattered, 

 sharp, microtubercles. On the surface of the peduncular part of the body, 

 only a few pinuli remain, and over much of the dermal surface they have 

 been lost. On the gastral surface and on the uninjured parts of the dermal 

 surface, they are thickly crowded. 



In the walls of the larger canals a few canalar pinuli are to be found. 

 They are of the same general type as the dermal and gastral pinuli, but 

 with a shorter and relatively more slender distal ray. 



Macramphidiscs of the type shown in Fig. 2, Plate 3, are very 

 abundant in the dermal and gastral membranes. The shaft is smooth, and 

 the umbels closely approach the equator of the spicule. The umbels are 

 wide, evenly rounded, not truncated apically, and include 8 tongue-shaped 

 rays, which are rounded at the free end. A typical spicule has the follow- 

 ing measurements: total length of spicule, 160 \l ; width of umbel, 100 /x; 

 depth of umbel, 70 /x; greatest width of umbel ray, 24 /x. The total length 

 of the spicule commonly varies from 120 to 180 /x, but larger spicules are 

 exceptionally found which reach a length of 200 to 250 /x. The umbel 

 rays are sometimes not strictly rounded at the free end, but round-pointed, 

 and occasionally even sharp-pointed. 



Mesamphidiscs having the character shown in Fig. 6, Plate 3, are 





