314 
THE VOYAGE OF H.M.S. CHALLENGER. 
Remarks. — This little sponge, 11 by 10 mm. in diameter, and 10 mm. high, is the 
only representative of Zittel’s Megamorina in the Challenger collection. The family 
is chiefly known in the fossil state ; only one existing species has been described pre- 
viously to this, and that — -Lyidium torquila, 0. Schmidt — evidently belonging to a 
difierent species, or, if the published descriptions are complete, to a difierent genus, 
and perhaps family, since it is represented as not possessing triaenes, microxeas, or 
spirasters. 
Owing to the precious nature of the small amount of material I had at my disposal, 
I could not make quite so searching an investigation as I could have wished ; at the 
same time, few points capable of determination have been left obscure. Most doubtful 
are the characters of the oscules and pores, but such few apertures as I did And of either 
kind were small, simple, and circular, not sieve-like. 
The ectosome (PI. XXXIII. flg. 9), about 0'6 mm. in thickness on the upper surface of 
the sponge, consists of a tender collenchyma containing numerous round or oval hollow 
cells, 0’02 to 0‘023 mm. in diameter, with thin structureless walls and scanty granular 
protoplasmic contents, not taking a deep stain with reagents. A circular or annular 
nucleus, 0'004 mm. in diameter, lies embedded in the protoplasm, which is vacuolated. 
The illustration (PI. XXXIII. flg. 13) shows these cells in the collenchyma imme- 
diately beneath the outer epithelium ; the wash of brown colour represents the collen- 
chymatous matrix, which is not a solid mass as this would seem to suggest, but cavernous. 
The microxeas form quite a felt about the subderm al canals, much in the same fashion as 
in Poecillastra (PI. XXXIII. flg. 9). 
Choanosome. — The mesoderm, except in the vicinity of the larger canals, where it 
becomes collenchymatous, is a richly granular sarcenchyma, which takes a deep stain with 
reagents. Numerous small round or oval cells, 0‘02 mm. in diameter, with a nucleus 
0‘005 mm. in diameter, and resembling the vesicular cells of the ectosome, occur dis- 
persed through it, each cell lying within a little cavity, produced no doubt by treatment. 
Sometimes these cells, instead of presenting a faintly stained protoplasm surrounding a 
thin structureless wall, are wholly composed of protoplasm which takes an unusually 
deep stain. In some cases a number of little, transparent, structureless, somewhat highly 
refractive, globules are seen surrounding the margins of both the deeply and faintly 
staining cells; they look somewhat like oil drops (PI. XXXIII. flg. 14). Of their real 
nature I am ignorant. The flagellated chambers are large, 0‘044 mm. wide by 0'04 mm. 
long, almost spherical, provided with a wide prosopyle, 0‘02 mm. in diameter, and an 
also wdde apopyle, 0‘0237 mm. in diameter, which leads into an aphodus frequently as 
wide as it is long, sometimes, for instance, measuring 0’0275 mm. in both directions 
(PI. XXXIII. flg. 10). 
The choanocytes are large, frequently O’OllS mm. in length, and sometimes nearly 
0'004 mm. in diameter at the base. The collar or collum, I am not rightly sure which 
