SILICIOUS AND HORNY SPONGES WILSON. 415 



abundant small afferent canals are seen beneath the dermal mem- 

 brane, giving the surface a vaguely porous appearance. Wall of 

 cloaca covered with the closely set apertures of efferent canals ; these 

 apertures not closed in by membrane, 1.5 mm. to a fraction of 1 mm. 

 in diameter. Sponges, taken in February, are full of embryos. 



The main skeleton includes ascending primary fibers which curve 

 outward toward the surface, branching as they go, thus becoming 

 radial. Between these are stretched primary connectives, the ar- 

 rangement producing large squarish or rectangular meshes visible 

 to the eye about 300-600 |jl wide. These meshes are subdivided into 

 smaller ones, 100-200 \l wide, by reticula of finer secondary connec- 

 tives. Primary fibers close to cloacal wall, about 120 pu thick, 

 diminishing to a thickness of 100-50 y. as they approach outer sur- 

 face, usually less than 50 [x thick at the surface. Except at the 

 surface the spongin of the fibers is very abundant, the spicules chiefly 

 but not absolutely confined to a loose core about one-third the thick- 

 ness of the fiber. At the surface, while the fibers remain pluri- 

 spicular, the spongin is comparatively scanty. 



The primary connectives are like the main fibers, although in gen- 

 eral somewhat slenderer, 70-100 [h thick. The secondary connectives 

 are slenderer than the primary, grading down to a thickness of about 

 12 [a; spongin abundant, spicules forming a core one to a few rows 

 wide. 



Fibers of dermal skeletal reticulum for the most part very slender, 

 10-28 \j. thick, ranging from unispicular to such as contain a few 

 rows of spicules; spongin abundant. Thicker fibers may actually 

 form a part of this reticulum but most of the thick fibers seen in 

 surface view are subdermal. Perhaps the precise condition in any 

 one spot is not constant during growth changes. Meshes of dermal 

 reticulum mostly 175-350 [/. wide, 4-sided or polygonal. From the 

 fibers of the reticulum, not only at the nodes but between them, short 

 tufts of spicules project radially outward. Some of these represent 

 the ends of radial skeletal fibers, but others do not. They all pro- 

 ject just beyond the dermal surface and include from 2-3 to a con- 

 siderable number of spicules. 



The spicule is a small slender oxea, 80 by 3 \l. 



The habitus, regularity in arrangement of the main fibers and pri- 

 mary connectives, thickness of fibers, character of fiber, size of oxea r 

 all show that the Albatross sponges can not be separated from 

 Siphonochalina crassifibra described by Dendy (1889) from the 

 Gulf of Manaar (Ceylon). There is only one point of difference. 

 In Dendy's sponges there are only (numerous) scattered spicules 

 between the primary connectives, whereas in the Albatross specimens 

 such spicules are cemented together and form secondary reticula. 



