SPONGES 63 
On the other hand, in a sponge of the genus Tuba, the Finger Sponge, 
ef which I have given a cut on page 42, Fig. 27, the upper figure being size of 
life of a single tube, andthe lower of a cluster of tubes reduced, a section 
through the sponge shows the water system clearly. Here, however, there do 
not appear to be anydistinct excurrent openings. ‘The whole outer surface of 
the sponge is covered with a kind of closely fitted fiber through which water 
is admitted to the water system within. This consists of a series of cells which 
are either continuous orare closely connected by tubes, one. within the other, 
so that the whole system passes directly through to the excurrent openings, 
which open into the large central tube, much as does the water system in the 
Tube Sponge. (See page 11 to 15, and Figs. 2, 3 and 9. ) 
The cilia cells are, as a rule, smaller than in Horny Sponges. Here in 
them we also find the typical collar cells, which will probably also be found to 
occur inall sponges. These cells surround the upper part of the psendopoda- 
like process which I have givenin fig. 5, page 15, and from them are thrust 
out long, whip-like cilia which are constantly in motion, and which not only 
cause the fiow of water through the tubular system of the sponge, but which 
also gather food from this water, and by withdrawing, carry it into the interi- 
or of the psuedopoda-like prozess, where it is passed into walls of the eavity to 
become absorbed, much as food is passed into the body of the amoeba. When 
the nutritious matter contained in this food is digested, the refuse matter is 
passed out and flows onward with the water, and out of the excurrent openings, 
See Figs. 2 and 3, c, c, page 13, | 
