SPONGES — WHITELEGGB. 489 



Isochelse of the Clathria type, confined to the thin dermal 

 membrane; size 0"014. 



This species is remarkable on account of the complete union 

 of the gorgonoid with the sponge. Ft was only after a prolonged 

 study of many sections that I realised its true significance. A 

 fortunate section cut transversely displays the intimate union 

 of the two organisms. The following is a brief description of 

 the principal f^^atures as seen in amounted section. The central 

 cavity of the stem of the gorgonoid is nbout 1 mm. in diameter, 

 and tlie wall of spicules is 0-1 mm. in thickness ; laterally a bud 

 is given off and measures 5 mm. in length and 1-2 mm. in 

 diameter. The retractor muscles are plainly visible, together 

 with several long vermiform mesenteric filaments. The mesen- 

 teries are also present in the main axis, and outside its walls 

 there is no trace of the sarcode of the gorgonoid. The spicular 

 walls are strongly contracted at the base of the tentacular crown, 

 but again expand for a short distance and then converge to the 

 small polyp aperture. The latter is surrounded by a layer of 

 sponge, about 0'2 mm. in thickness. The sponge presents a series 

 of echinating spicules which have their bases imbedded in the 

 walls of the gorgonoid. Many are at right angles, but others are 

 sub-parallel and finally united in a compact bundle which on 

 approaching the surface branch several times, and ultimately 

 form wide funnel-shaped tufts at the surface. The bases of the 

 spicules are in close contact ; at the ends of the secondary 

 branches, their apices are widely divergent and all attain to 

 nearly the same level. There are a few proper styli arranged 

 transversely to the spicular tufts, but the majority of the binding 

 spicules are of foreign origin. The space between the gorgonoid 

 and the surface of the sponge is charged with fine brown granu- 

 losa matter, and the large subdermal spaces are more or less 

 occu})ied by oval bodies, which are probably the gemmules of the 

 sponge. They consist of a series of well defined cells, and 

 measure about 0-15 by 0-1 mm. The collar at the base of the 

 tentacles is composed of curved spiny blunt-ended spicules about 

 0"25 mm. in length. The tentacles are supported by numerous 

 fusiform sp cules, which are feebly spined and measure 0*3 to 

 25 in length. 



D END ORYX, Grmj* 



DENDOPvYX MIRABILIS, sp. nov. 



Station 47. 



Sponge in crusting, growing on a large, branched, papyraceous 



worm colony. It forms around the tubes a layer of about a 



quarter of an inch in thickness. The surface is very porous and 



furnished with scattered circular oscula — about 1 mm. in 



* See Part 9, p. 480. 



