SPONGES jo 
A small, short-legged crustacean also occurs in the water system of the 
‘Tube Sponge, and a small species of sea weed is quite often found attached to 
old sponges. 
SPICULIGENOUS SPONGES. 
As already remarked en page 9, that although the sponges which are 
provided with spicules, are usually separated by specialists from the Horny 
Sponges which are without spicules, which are produced by themselves, the 
division is hardly a natural one, for there are a number of species which are 
direct intergrades between the two groups. But as there area great number 
of sponges which do not have spicules, and a larger number which very decid- 
edly do have, it is perhaps as well te group sponges as Horny and Spiculig- 
venous, 
Spiculigenous Spenges then, as a rule, differ from Herny in having the 
horny fibers more or less supplemented by spicules. These spicules vary in 
number from sponges in which they are scattered sparingly through the horny 
matter, to species which are wholly made up of spicules. 
Examples of spicules may be seen in Figs. 31 and 32. Therecan be no 
doubt but what the use of these spicules is defensive, that is, they prevent the 
inroads of parasites. Although, as will be seen by referring under the head- 
ing Parasites of Spiculigenous Sponges, these sponges are not quite free from 
parasites, yet I have never seen a sponge of this species which contained any 
parasitical worms of any kind. ohh 
The Spiculigenous Sponges may be divided into two groups which are 
