TRANSACTIONS. 
On the Organization of Grantia ciliata. 
By J. S. BowERBANK, LL.D., F.R.S., L.S., &c. (PL V.) 
(Read March 30th, 1859.) 
Some years since, I had tlie honour of reading before this 
Society a paper On the Ciliary Action of the Spongiadse/' 
which was subsequently published in the ^ Trans, of the 
Micr. Soc./ vol. iii_, p. 137. In this communication the sub- 
ject of investigation was Grantia compressa. This sponge, 
which is of a compressed saccular form, has its parietes con- 
structed of a series of large, angular interstitial cells, disposed 
at right angles to the long axis of the sponge, and these 
cells are lined with minute tesselated cells, each being fur- 
nished with a single cilium. The action of these cilia, lashing 
slowly backward towards the distal end of the interstitial cell, 
and rapidly forward toward the proximal end, induces at the 
same time the imbibition of the surrounding water through 
the porous system at the surface of the sponge, and the ex- 
pulsion of the excurrent faecal streams through the oscula 
at the proximal end of each cell into the great cloacal cavity 
in the middle of the sponge, and which extends from its base 
to its apex, whence the fsecal stream is discharged. To this 
extent I was enabled to trace the vital actions of inhalation 
and exhalation, and to verify the admirable observations of 
Dr. Grant on these subjects; but from the nature of the 
sponge under examination, I was unable to obtain a view of 
the porous system, nor could I detect any positive action in 
the oscula during the course of the rapid passage of the 
excurrent stream through these orifices ; but on a subsequent 
occasion I was enabled to satisfy myself that both the oscula 
and the pores in other species of Spongiadse were capable of 
being partially or entirely opened or closed at the will of the 
animal, and that there were two conditions of inhalation and 
exhalation, beside a state of complete repose ; the first con- 
dition being gentle and continuous, and equivalent to the 
operation of breathing in the higher classes of animals, while 
the second was rapid and forcible, and is analogous to the 
VOL. VII. h 
