76 Journal of the Asiatic Society of Bengal. (January, 1913. 
total oscular area) is invariably increased owing to the appear- 
ance of oscula on areas from which they were previously absent. 
This is apparently due to the fact that the sponge experi- 
ences difficulty, in unnatural surroundings, in getting rid of 
waste or extraneous matter. Barrois’s heavily parasitized 
that Nudospongilla aster, which inhabits the same environment 
as C. barroisi, is a peculiarly compact sponge without any trace 
of a central cavity is noteworthy: but it is not unusual for two 
species that live together to adopt diametrically opposite means 
to attain the same end, and if the particularly well-developed 
exhalent system implied in the production of a central cavity 
opening by a large osculum, is advantageous in getting rid of 
silt that has entered the sponge, a compact structure may be 
equally efficient im preventing the silt from entering at all. 
e other main peculiarity of Cortispongilla, viz. the skele- 
tal cortex, renders the sponge harder and less friable than it 
would otherwise be, but I have no suggestion to offer as to the 
precise reason why its development should be particularly 
acvantageous to this genus. An interesting point is its analogy 
to the skeletal cortex of the freshwater species of the genus 
Veluspa in Lake Baikal. Possibly the cortex performs a similar 
function in the two genera. In Veluspa, as has already been 
noted, it is produced by a splaying out of the extremities of 
the vertical skeleton-fibres, whereas in Cortispongilla it is due 
to an agglomeration of fibres a short distance within the sponge. 
In the species of Veluspa chosen for illustration (pl. iv, fig. 5) 
the difference is, however, more clearly seen than it is in some 
beca 
well developed and the vertical fibres are very distinct one 
from another even at their distal extremities. 
as yet of the lower invertebrates of fresh water of other parts 
of Western Asia or of North Africa. The sponges of te ake 
= iT a a etal he 
OS ea ee 
a 
