150 BRITISH SPONGES: 



These spiciila have apparently no constant or ordinate arrange- 

 ment, but, accordmg to Dr Grant, they are " placed like a 

 frame-work round all the openings, in the order best calculated 

 to prevent these passages from changing their dimensions." 

 They are all of the same form and mostly of one size, linear, 

 very slightly and regularly curved and acutely pointed at both 

 ends. Dr Grant describes them as being cylindrical and tubu- 

 lar, and such they have appeared to be to us, but Raspail says 

 that they constitute solid six-sided prisms. " If these bodies 

 were tubular," he adds, " it is evident that when placed in water 

 after having been broken in the air, their median line would be 

 black instead of white, on account of the difference of the refrac- 

 tive powers of its internal capacity ; but this illusion is destroy- 

 ed by simply cutting the crystal across somewhat obliquely, in 

 which case a dark and homogeneous base is presented." New 

 System of Organic Chemistry, p. 543-4, pi. 12, fig. 1-5. 



The soft gelatinous matter which fills the interstices of the 

 sponge consists of a colourless glairy fluid, filled with minute 

 transparent granules. Where this matter lines the canals or 

 surface, and where it is exposed to the friction of the circum- 

 fluent water, it is protected by a delicate and diaphanous pellicle 

 or skin. * The granules lie underneath, but at certain seasons, 

 either from the expulsive appetency of maturitv, or from the 

 decay of portions of the common mass, thev are sepax'ated from 

 it, and are the means of difi"using and continuing the species. 

 When first set free from their gelatinous soluble matrix they 

 are endowed with a distinct power of locomotion, and in liveli- 

 ness and mobility rival the infusorian animalcules, with which 



* This skin is particularly described by Dutrochet and Hogg. Dr 

 Grant says, — " Tlie soft matter of the Spongilla does not seem to pos- 

 sess a distinct membiaiioiis coat, but is a little more consistent, and has 

 a glistening surface, wherever it is in contact with the element in which 

 it lives, as within Uie canals, and on the outer surface of the body." 



