AND PHTSIOLO&Y OF THE SPONGIAD^. 
807 
a longitudinal section of the intermarginal cavities of Grantia com/pressa with the cilia 
in situ. A \dew of the small portion of the inner surface of the sponge, exhibiting the 
oscular orifices and the appearance of the cilia in motion within them, and detached 
cilia and cells from the same sponge, are also represented by figs. 1, 2, 3 & 4, Plate 
XXXIII. 
In the course of my endeavours to detect the cilia in Halichondroid sponges, I have 
frequently observed, in slices of the sponge taken from the surface, that the incurrent 
action has continued for a considerable period, while in sections of the same sponge 
taken from deep amid the tissues no such action of the currents could be detected. In 
sections from the surface in which the inhaling process was in vigorous condition, when 
the inside of the section was examined, that peculiar flickering appearance was often 
visible in the cavities immediately beneath the dermal membrane which is so characteristic 
of minute cilia in very rapid motion ; and although many molecules were rushing inward 
with considerable velocity, others might be seen which continually waved from side to 
side but made no progress forward ; in fact they presented precisely the appearance that 
I have described as taking place in the oscula of the proximal ends of the great inter- 
marginal cells of Grantia compressa', and I have no doubt, in my own mind, that those 
of the Halichondroid sponges were also extraneous particles of matter adhering to the 
apices of the minute cilia, rendering their motions apparent, while the cilia themselves 
were perfectly invisible. 
Caetee, in his paper on “ Zoosperms in Spongilla,'" published in the ‘Annals and 
Mag. Nat. Hist.’ vol. xiv. Second Series, p. 334, describes ciliated bodies from di Spongilla 
from the water-tanks of Bombay, somewhat similar to those of Grantia compressa., but 
the basal cell appears to be proportionally larger and the cilium shorter than in those 
of G. compressa. The author, in describing the detached cells and cilia, says, “ At first 
the polymorphism of the cell and movements of the tail are so rapid, that, literally, 
neither ‘ head nor tail ’ can be made out of the little mass. Presently, however, its 
power of progression and motion begins to fail, and if separated from other fragments it 
soon becomes stationary, and after a little polymorphism assumes its natural passive 
form, which is that of a spherical cell. During this time the motions of the tail become 
more and more languid, and at length cease altogether.” The author continues, “ If, 
on the other hand, there be very large fragments in the immediate neighbourhood, or 
an active sponge-cell under polymorphism sweeps over the field, it may attach itself to 
one or the other of these, when its cell becomes undistinguishable from the common 
mass, and the tail floating and undulating outwards is all that remains visible.” This 
observation is important, as it accounts in a great measure for our inability to find the 
cilia in situ in the living and active condition of the 8pongilla ; and if the structure and 
imbedment of the basal cell in the marine sponges be like those in that genus, the same 
results would probably arise in the marine species, rendering it extremely difficult, if 
not impossible, to detect these organs in situ and in action. 
Liebeekuhn, in his paper in Mullee’s ‘Archiv,’ 1856, pp. 1-19, 319-414, gives an 
