64 SPONGES 
This arrangement of cilia may be seen by referring to Fig. 37, where [ 
vive an ideal section of one of these cells, greatly enlarged, with the numerous 
cilia, andin Fig. 38 is given a much more enlarged cut of a single whip cell, 
and its long, slender process known technically as the flagellum ; A, B is the 
thin collar, C, the base of the whip cell into which the food is passed for di- 
vestion. 
BP 
As already remarked, it is the motion of these cilia whieh draw the water 
Fig. 36. Fig. 35. 
Section of Finger Sponge Spiculigenous Sponge. A, 
showing water system. excurrent openings ; B, sec- 
tion of outer portion, both 
enlarged, 
into the tubular system through the incurrent tubes, and expel it out af the ex- 
current tubes. 
FORMS OF SILICIOUS SPONGES. 
Sponges of this group which occur in salt water, are quite variable, and 
their method of growth is also quite variable, On page 31 I give a figure ofa 
