140 THE SPONGES. 



which seem to be particles of echinoderm spines. The massive part of 

 the specimen is 70 mm. wide, 30 mm. thick, and 40 mm. high. 



Tlie surface exhibits numerous vestibular spaces, appearing as elongated, 

 irregularly tubular cavities, often branching, extending tangentially beneath 

 the surface, and separated from the exterior only by thin dermal membrane. 

 One of the largest of these spaces is shown in Fig. 1, Plate 19, to the 

 left. The transverse diameter of such spaces varies from about 1 to 4 mm. 

 The length, which is often difficult to measure, owing to the meandering 

 course of many of the spaces, is frequently 10 to 20 mm. At one end 

 many, probably all, of the spaces communicate with the exterior through 

 an osculuin 1 to 4 ram. in diameter. (The surface of the sponge is injured 

 here and there, and the natural apertures are not everywhere discernible 

 with certainty.) The membranous covering of the spaces is moreover 

 perforated here and there by apertures 85 to 200 fi in diameter, scattered 

 singly, or in small groups. At the non-oscular end the vestibular spaces 

 lose themselves in the more solid sponge tissue. The spaces are larger 

 and comparatively far apart in the massive part of the sponge body, 

 smaller and mucli more abundant where the sponge is spreading over a 

 loose, broken substratum. 



The surface of the sponge between the vestibular spaces appears to the 

 eye dotted with small, round areas, about 0.5 nun. in diameter. Those 

 vary greatly in abundance, being in places 1 to 2 mm. apart, but again 

 only scantily scattered. They are perforated membranes roofing in canals 

 of corresponding size, which pass radially into the interior. The mem- 

 branes for the most part contain several apertures, but sometimes only 

 one, which probably are to be regarded as oscula. 



The dermal membrane in general is riddled with thickly strewn pores, 

 which vary considerably in size, the diameter ranging at any rate from 85 

 to 220 /A. Small subdermal cavities everywhere underlie the dermal mem- 

 brane. The flagellated chambers are 32-36 fi in diameter, and are 



crowded together in regions which are separated by collenchymatous 

 tracts, the latter traversed by the larger canals. The arrangement of 

 the chambers in the trabeculae of the sponge indicates that they are 



eurypylous. The color is a light yellowish-brown^ the membranes 



roofing in the vestibular spaces appearing translucent and darker than 

 the general surface, when the body is iunnersed. The sponge, while 

 moderately firm, is exceedingly fragile, owing to its great brittleness. 



