208 Prof. H. James-Clark on the Spongie ciliate 
is broadly rounded, at the sides lightly indented and irregu- 
larly polygonal by mutual contact with others, and eed 
in front into a delicate, membranous, circular collar (b 5), 
which might be compared to a transverse section of a tube 
which is about as long as it is broad. This collar is capable 
of variations in form, like that of Codosiga (§ 6) and Salpin- 
geca (§§ 7, 8, 9), at one moment assuming a truncate conical 
shape (figs. 43, 44,6), and in the next instant, expanding its 
distal margin into a distinct flare (fig. 42, b) which is at least 
two-thirds as wide as the body; or, finally, it retracts alto- 
gether an@ disappears for a while, but eventually reappears 
and expands to its fullest dimensions*. 
The flagellum (fl) is the only prehensile organ which the 
monad possesses. It arises from the middle of the frontal area, 
and extends to a great length, at least five or six times as long’ 
as the body, with scarcely any diminution in thickness. It is 
a comparatively thick filament, and quite conspicuous, on 
which account it is so easily seen through the whole mass of 
the colony. It usually vibrates with considerable vigour from 
base to tip, but occasionally assumes the quiescent state and 
arcuate form so eminently characteristic of that of Codosiga 
(§ 6), Bicoseca (§ 3), and others. | 
The mouth is the only organ which has not been actually 
observed, although its position has been inferred, not only 
from the otherwise similar structure of the monad of this crea- 
ture to that of Codosiga.(§ 6), but because currents of floating 
particles are constantly whirled in by the flagellum and made 
to impinge upon the area within the collar. In addition to 
this it may be added that more or less numerous coarse and 
fine particles (fig. 44,@) are always present and scattered irregu- 
larly about the interior of the monads, apparently under various 
degrees of digestive decomposition. | 
The contractile vesicles (cv) are two in number, and lie near 
_ ™* Tn this connexion it may be well to mention the latest decision of 
Carter in regard tothe structure of the monociliated sponge-cell. In the 
Annals and Magazine of Natural History, vol. xx. 1857 , pl. 1. figs. 10, 
11, this cell is —— as an oval body, with a single ciliary appen- 
dage; but in a subsequent communication to the same periodical (vai: iii. 
1859, p. 14, pl. 1. figs. 12, 18, 14), a partial recantation seems to be 
made, and the cell in question is figured with “‘two spines or ear-like 
oints projecting backwards, one on each side of the root of the cilium.” 
fe now, we suppose these “two spines”’ to be the right and left profiles 
of a membranous, cylindrical collar, such as I have described in - 
lenia, then it follows that the monociliated sponge-cell of Spongilla is like 
that of the former. That Carter did not always find these “‘ two spines,” 
may be explained by the fact that the membranous collar, as I am in- 
elined to believe the “ spines” to be, was retracted, since I have frequent] 
observed this to happen in the case of Leucosolenia when it was distu rie § 
