REPORT ON THE TETRACTINELLIDA. 
77 
The abundant development of collenchyme leads to a marked decrease in the number 
of flagellated chambers, and, in accordance with a very general rule, to a decrease in size 
also. They still, however, remain eurypylous, the apopyle measuring about 0‘012 mm. in 
diameter. They lie in immediate contact with the walls of the smaller incurrent canals, 
which, devoid of any marked collenchymatous investment, and surrounded with flagellated 
chambers, can be traced into the midst of a mass of collenchyme bounded externally by 
two excurrent canals. The smaller excurrent canals, on the other hand, excavate the 
collenchyme which bes on the excurrent side of the chambers. The chambers and the 
smaller canals are frequently filled with a granular material which stains with eosin and 
gives a very dirty appearance to sections ; it would appear to be food in process of 
digestion or egestion. 
With regard to the arrangement and distribution of the microscleres, it may be noted 
that the plesiaster is confined chiefly to the neighbourhood of the flagellated chambers, 
seldom extending into the collenchymatous walls of the canals ; the metasters are chiefly 
scattered in a layer beneath the epithelium of the canals, and the spirasters are chiefly 
confined to the under surface of the epithelium of the surface of the subdermal 
cavities. 
The figure given of the metaster (PI. VI. fig. 7) is not characteristic, and I regret 
that no illustration appears of the spiraster ; in its absence I would refer as an excellent 
substitute to that of the spiraster of Dactylocalyx masoni given by Bowerbank.^ 
Thenea sp. (PI. VIII. fig. 23). 
Sponge (PI. VIII. fig. 23). — Small, ovate ; surface hispid ; excurrent canals opening in 
a cribriform area which occupies the summit, and which is surrounded by a marginal 
fringe of long oxea ; incurrent canals communicate with the exterior by pores generally 
dispersed ; no specialised poriferous area ; base marginally fringed with projecting 
spicules, the distal ends of which are broken off. 
Spicules . — I. Megascleres. 1. Oxea, cylindrical with pointed ends ; no unbroken 
specimens met with ; 0*044 mm. in diameter. 
2. Protrisene, a stout cylindrical rhabdome, proximal end not seen ; cladi stout 
and long, curving outwards and forwards at first, then forwards only, or forwards and 
slightly inwards ; diameter of rhabdome 0*055 mm., cladi 0*95 by 0*043 mm., chord 0*7 mm. 
3. Dichotrisene, of the usual form; protocladi 0*18 by 0*045 mm.; deuterocladi 
0*93 by 0*039 mm. 
4. Anatrisene, a cylindrical rhabdome with a sharply pointed end ; cladi diverging 
outwards and backwards; rhabdome 2*71 and longer by 0*013 mm. ; cladi 0*24 mm. 
long ; chord 0*24 mm. 
1 Proc. Zool. Soc. Land., pi. vi. fig. 4, 1869. 
