10 SPONGES 
removed from the water, and usually become black, a color which the majority 
of species assume when dried with the flesh on the skeleton. 
Upon examining a living sponge, it will be found that there are two 
kinds of orifices ; first, a large number of small ones which are quite uniform 
in size. These are the incurrent orifices, through which the water is taken 
into the interior of the sponge. Second, we find a smaller number of larger 
orifices which are rather irregular in size, some being much larger than others. 
These are the excurrent orifices, from which the water passes out of the sponge 
afte: it has circulated through the interior. 
Some sponges are tubular in form, with a few excurrent orifices, some- 
times with one only. Such sponges are rather more simple in structwe, and 
their organism can be much more readily understood by a beginner than if a 
sponge of more complicated structure is taken. Such a species may be found 
in the Tub2 Sponge, of the genus Verongia which I will take as an example 
in explaining what is known as the water system. 
‘The Tube Sponges are large, prominent sponges, with the form cylin- 
(rical and tubular for their entire length. See plates 1 and II. Tube, oc- 
cupying more than one half the diameter of the sponge, hence the walls are 
only moderately thick. Outer surface roughened by circular projections, that 
extend outward about one half the thickness: of the walls. 
_ Srrucrure. ‘In life this species is fleshy, yet is soft and compressible, 
but when dried with the sarco&) on, it is very rigid. The water system is .com- 
paratively simple. ~ On the outer surface of the sponge, are small tubercules 
about .05 in diameter (all measurements are in inches and in hundredths of 
inches ) by abdut .01 high. In the center of each of these tubercules is an op- 
ening, some .02 in diameter. This opens into a cylindrical tube some .10 long 
The walls of this tube are composed of rather tougher material than the lining 
