218 SYSTEMATIC ZOOLOGY FOR TEACHERS. 



106, where a single tube is given to more complicated structures, like the 

 logger-head sponge, fig. 101, and the scarlet sponge fig. 102, up to the com- 

 mercial sponges. 



Taking a step in another direction, we find that the tube sponges £re 

 not all alike in diameter. While some g:o\v small and slender, others pro- 

 duce cylinders which are mare cup like. For example, compare the sponge 

 figured on page 178 "with that given on plate VIII. This leads us to a group 

 of form; which have the exeurreiit tube, or cloical opening, very large. These 



Fig. 100. 



Tube Sponge. 



are the cup sponges. And a species quite nearly related to the tube sponge 

 is the giant cup, ( seefig. 103) a sponge which grows to the height of two 

 feet or more and nearly as much in diameter. Two other forms of cup 

 sponges are given in figs. 104, 105, but these are not &t all closely related to 

 either the giant cup or to the tube sponge. They are, in fact, spiculigenous 

 sponges, and they may have had their origin in such a form of spiculigenous 

 tube sponge, as the finger sponge given on page 183, fig. 85, which grows 

 singly and also in groups. This form of spiculigenous sponge is exceedingly 

 variable in the diameter of the tubes, some being found an inch across, while 

 others occur which are five or six inches wide at the top tapering to the 

 baes, and are thus perfect cups 



