796 
DE. J. S. BOWERBANK ON THE ANATO^klT 
accordance with the variations in the actions of the sponge. Thus in littoral sponges 
they are frequently entirely closed, and their situation even quite indeterminable, during 
the period of their exposure to the air ; but when immersed in water, and the sponge is 
in the energetic action of the imbibition of nutriment, they are expanded to them f ull 
extent ; but when this action ceases and that of gentle respiration only exists, many of 
them close entirely, and others exhibit apertures not exceeding half their former diameter 
while the imbibition of nutriment was in vivid action, Thek expansion or contraction 
is not rhythmical ; each can be opened or closed at the will of the sponge without any 
apparent effect on the others. Nor is the habit of opening and closing the oscula the 
same in every species. Thus in the course of my observations on HaliclionclHa jjcmicea 
and Hymeniacidon carmicida in their natural and undisturbed localities, I have frequently 
observed, during their exposure to the air at low tide, that while no oscula in an open 
condition could be found va. Hymeniacidon carunciila^ the greater portion of those on the 
specimens of Halicliondria 'panicea were more or less in an open state. 
They appear also to be subject to a considerable amount of modification as regards 
situation, even in the same sponge. Thus in our common British species, Halichondna 
panicea, when of small size, they are situated on the surface of the sponge, and are 
scarcely, if at all, elevated above the dermal surface ; while in large specimens of the 
same species we find them collected in the insides of large elongated tubular projections 
or common cloacse, and these organs vary from a few lines only in height and diameter 
to tubular projections several inches in height, with an internal diameter of half or three-- 
fourths of an inch. When they attain such dimensions their parietes are often of con- 
siderable thickness, and their external surface becomes a,n inhalant one, like that of the 
body of the sponge. 
In many species the oscula are always elevated above the dermal surface, and these 
thin pellucid elevations are permanent, while in others, as in Spongilla fiumatilis, the 
tube exists only during the course of the energetic excurrent action ; and in such cases 
it appears to be subject to great variation in size and form, as I have shown in the 
description of Spongilla in my “Further Eeport on the Vitality of the Spongiadse,” 
in the volume of the Keports of the British Association for 1857. 
Inhalation and Exhalation. 
The works of the old writers on Natural History are full of vague opinions on the 
nature of sponges, but none of them seem to have seriously studied their anatomy, or to 
have kept them alive in sea-water and examined their daily habits. They appear to 
have excited abundant attention in the closet, and but very little in their natural 
localities. The ideas of those authors are so loose and indefinite that it would really 
be a loss of time to seriously examine and attempt to refute them ; and as Dr. JoHNSTOiif, 
in his ‘ History of British Sponges,’ has given in his Introduction, Chapter 2, an excellent 
digest of the various opinions of the previous writers on the subject, I shall content 
myself with referring my readers to the work of that eminent author for further informa- 
