FRESH-WATEIl SPONGES. 88 



have been seen and sketched by many reliable investigators. For 

 more extended remarks on this branch of the subject the student 

 is recommended to the fifth chapter of W. Saville Kent's " Manual 

 of the Infusoria,'' where the affinities of the sponges is fully 

 discussed. 



The skeletons of all the fresh-water sponges are made up of 

 siliceous spicula, generally slightly curved, and pointed at both 

 ends. These spicula are sometimes smooth, frequently slightly 

 micro-spined, and, at times, roughly spined, varying in form and 

 size in different species. Besides the skeleton spicula, in some 

 species there are fine dermal spicula, which are mostly spined and 

 finely pointed. In a few species, small and delicate birotulate 

 dermal spicula are found in great abundance. 



The great distinguishing feature between the fresh-water 

 sponges and those of marine origin is the presence, in the former, 

 of little seed-like bodies, large enough to be seen with the naked 

 eye. These are a sort of winter egg, or resting spore, for the 

 preservation of the species through the changes incident to fresh- 

 water in winter. They have been called by various names, as 

 gemmulae, ovaria, and statoblasts. This last, by Mr. Carter 

 (perhaps the greatest authority on the sponges), is in keeping with 

 the name given to bodies of a similar character, found in the 

 fresh-water polyzoa. 



The walls of the statoblasts are made up of, and strengthened 

 by, siliceous spicula of peculiar form. In some species they are 

 birotulate, placed side by side, radially, in the wall of the state- 

 blast. In other species they are small spined spicula, placed 

 tangentially on and in the wall. In others, they are trumpet- 

 shaped {Tubelld), or shield-shaped {parmula). It is principally 

 by the position and form of these minute spicula that genera and 

 species are determined. But there are exceptions, as in the genus 

 Carter ins of Potts and Mills, where the foramen al opening of the 

 seed-like body is prolonged, either by a tube, terminating in short 

 cirrous processes, as in C. iubisperma, Mills, or by long tendril- 

 like processes, as in C. tefwsperma, Potts, and others of that genus. 

 The generic name of one of the first known of the fresh-water 

 sponges has been given in honour of Meyen, a German Spongolo- 

 gist, who, in 1839, first pointed out the use and position of the 



