BowEKBANK^ oYi Gvantia ciliata. 
83 
energetic nutrimental action commences^ every osculum pours 
forth a powerful stream into the cloaca, and the expansive 
force of the current thus produced distends the neck of that 
organ^ and speedily changes its somewhat truncated conical 
form into a cylindrical one^ and the elongated cone of ciliary 
spicula also becomes changed into a cylindrical tube, through 
which the excurrent stream passes with considerable ra- 
pidity and force. 
Thus we see that the incurrent and the excurrent actions 
of this highly organized sponge are both effected on the 
same principle, with such modifications of structure in the 
respective organs as adapts each to its especial office. The 
amount and regularity of motion induced by the effects of 
ciliary action only, without apparently the slightest aid from 
nervous or muscular agency_, is truly remarkable. 
The defence of the interior of the sponge from the incur- 
sions of predaceous annelids and other enemies is not con- 
fined to the long ciliary fringe of spicula at the mouth of the 
cloaca^ nor to the spiculated, rectangular triradiate spicula 
of its mouth ; for we find on the inner surface of the cloaca 
spicular rays frequently projected from the equiangular tri- 
radiate spicula, with which it is abundantly lined. These 
rays are always more or less curved, and have their points 
directed towards the mouth of the cloaca. Dr. Grant de- 
tected these quadriradiate spicula in Grantia nivea many 
years since, during the course of his investigation of the cal- 
careous sponges, and mentioned them as one of the distinc- 
tive characters of G. nivea, but they are by no means peculiar 
to this species; but, on the contrary, they are found to a 
greater or a less extent in every calcareous sponge in which 
the oscula are discharged into a common cloaca. 
There is yet another mode of defence against any attempt 
at an entrance into the cloaca, which appears to be resorted 
to occasionally and under peculiar circumstances, and that is 
the capability of entirely closing the base of the neck of the 
cloaca by the extension of a membrane across its base. I 
have found this membrane in two cases, and in both of them 
it was not merely a clean film that might possibly have been 
formed by a small bubble of sarcode shed from the animal 
during or after death, but, like the other membranes of the 
sponge, there were numerous spicula imbedded in its surface, 
and in this, and in other respects of appearance and position, 
the membranes in both cases were alike. 
In conclusion, I may observe that not the least remarkable 
part of the history of this sponge is the number and variety 
of forms of spicula that compose its skeleton and defences, 
