BPICULA FROM SPONGES. 401 



Pachymatisma, Geodia, and many other marine species, a 

 very small quantity only is ever to be found, the substance 

 of each gemmule being almost entirely composed of 

 minute siliceous spicula ; if they be viewed when taken 

 fresh from the sponge, and also after removing the animal 

 matter by boiling in acid, a slight increase in trans- 

 parency is the only perceptible difference of appearance 

 noticed. 



Hyalonema, "Glass-Rope" Sponge. — A bundle of from 

 200 to 300 threads of transparent silica, glistening with a 

 satiny lustre like the most brilliant spun glass; each 

 thread is about eighteen inches long, in the middle the 

 thickness of a knitting needle, and gradually tapering 

 towards either end to a fine point ; the whole bundle 

 coiled like a strand of rope into a lengthened spiral, the 

 threads of the middle and lower portions remaining com- 

 pactly coiled by a permanent twist of the individual 

 threads; the upper portions of the coil frayed out, so 

 that the glassy threads stand separate from each other. 

 The spicules on the outside of the coil stretch its entire 

 length, each taking about two and a half turns of the 

 spiral. One of these long needles is about one-third of a 

 line in diameter in the centre, gradually tapering towards 

 either end. The spirally twisted portion of the needle 

 occupies rather more than the middle half of its entire 

 length. In the lower portion of the coil, which is em- 

 bedded in the sponge, the spicule becomes straight, and 

 tapers down to an extreme tenuity, ultimately becoming 

 so line that it is scarcely possible to trace it to its termi- 

 nation. 



"Many spicules of the awl-shaped and simple cross 

 types, especially short spicules, are met with within the 

 siliceous coil to its very centre, and, in cases where the 

 coil has been brought home without the sponge, such 

 needles can be shaken out from the interstices of the 

 threads. The spicules of Hyalonema are marked in their 

 character, and all the forms are found in all specimens of 

 the sponge imbedding the characteristic bundle of enor- 

 mous spicules ; so that there can be no reasonable doubt 

 of the specific identity of the sponge in all cases. 



11 Within the round apertures on the surface of the 



D D 



