PORIFERA OF THE L.M.B.C. DISTRICT. - AWE 
mm., and the deuterocladus from 0°037 to 0°045 mm. 
The orthotrizna are far less numerous and slightly smaller 
than the dichotriena. They are also placed close to the 
ectosome. The oxea are the most numerous spicules, and 
are arranged in bundles, which take their origin in or 
immediately beneath the region of the trizna, and stretch 
vertically down through the whole depth of the choano- 
some. Those oxea measure 0°34 to 1:5 mm. by 0°009 to 
0°026 mm. Amongst them we find a few stylote, strongy- 
lote and tylote spicules. E 
The microsclera are spherasters, 0°025 mm. in diameter, 
and spirasters 0°012 to 0°016 mm. in length. Besides 
those, I have found in some sections a third kind of 
microsclera, which looked like the fragments of the narrow 
blades of fret-saws, straight on one side, toothed on the 
other, and a few which were toothed on both sides (see 
fig. 2c, Pl. VII.). These spicules measure 0°08 mm. by 
0:0014 mm., but I do not think I have seen a complete 
spicule of this kind. They were found in the choanosome 
immediately beneath the ectosome. 
A great part of the choanosome, especially the portion 
in the neighbourhood of the ectosome, consists of a cys- 
tenchymatous tissue, also called vesicular connective tissue 
or bladder cells (‘“‘blasiges Bindegewebe” of German 
authors). It has been already remarked by other authors 
in various groups of the sponges, as by Vosmaer,* in Poly- 
mastia henispherica, by Sollast in Pachymatisma, &c., 
and also in some of the Lithistide. A similar tissue is 
known to occur in many Molluscs and in Tunicata.? 
* Vosmaer, ‘‘ Sponges of the Willem Barrents Expedition,” 1880 and 1881. 
** Bijdragen tot de Dierkunde.” 
+ Sollas, ‘‘ Report on the Tetractinellide, collected by H.M.S. Challenger,” 
p. XXXIx. 
= W. A. Herdman, ‘‘Report on the Tunicata, collected by H.M.S. 
Chalienger,” part i., p. 28—29. 
