﻿128 "ENDEAVOUR" SCIENTIFIC RESULTS. 



of the latter, that they proceed jruin the apex of the conulus, 

 and after running inwards, with gradually increasing diver- 

 gence, for a short distance towards the sponge-interior, 

 gradually curve round and return again to meet the surface 

 at varying distances from their starting point — the more cen- 

 trally situated fibres of the pencil proceeding to a further 

 distance than the more peripheral. Styli similar to those com- 

 posing the fibres are sparingly scattered through the tissues 

 together with discasters of two kinds, a larger and a smaller. 

 The former are closely aggregated in the immediate surround- 

 ing of all the main fibres encircling them as a kind of loose 

 sheath. The cortical skeleton is a layer of closely packed 

 discasters almost exclusively of the larger kind ; it is about 

 300 to 400 n in thickness. 



Megascleres. — These are styli, probably of a single kind — 

 the stouter with a more or less blunt or rounded distal ex- 

 tremity, and occasionally becoming almost perfectly stron- 

 gylote ; the slenderest usually sharply pointed. They are 

 sometimes elongately subtylote at the basal end, and have a 

 maximum size of 365 x 11 ji. 



Microscleres. — (i.) The larger discasters are stout spicules, 

 having a short central region devoid of spines, and on 

 either side of this two more or less distinct whorls of 

 large spines : those of the terminal whorl projecting 

 obliquely forwards; those of the sub-terminal, stand- 

 ing more or less perpendicularly to the spicule-axis. 

 They are about 40 jt in length (exclusive of spines), 

 and have a diameter in their spineless central region 

 of about 12 ;(. The spines are 10 to 12 ji long, 

 (ii.) The smaller discasters are very variable in form, no 

 two apparently being quite ahke. They are much 

 slenderer spicules than the preceding, with an elon- 

 gated spineless central region, and at either end, two 

 more or less distinct whorls of simple or (more usually) 

 compound spines, the latter of which are columnar in 

 form, with a few terminal spinules. The terminal 

 whorl of spines is often reduced and then appears as 

 a prolongation of the axis of the spicule. These 

 spicules are at most 38 ;t in length (inclusive of 

 spines), and have a diameter centrally of i to 4 fi 

 (rarely more than 2.5 }i). The stouter individuals 

 may represent a third kind of discaster intermediate 

 between the other two. 



Loc. — North coast of Tasmania, off Devonport. ("En- 

 deavour.") 



