MICROSCOPIC OBJECTS. 54 



Fig. 107. Spicula and Gemmules of Sponge (GeodiaBarreta), 



x200. 



Most sponges contain siliceous bodies called spicula (see 

 drawing) . They are of various forms ; but the most general 

 are acicular or needle-shaped, and stellate or star-shaped. 

 Most of the siliceous sponges also contain reproductive bodies 

 called gemmules ; they are the round masses in the drawing. 



Sponges also increase by ordinary ova, as in the case of 

 other animals. To separate the spicula, gemmules, &c. of 

 the siliceous sponges from the surrounding extraneous mass, 

 they must be boiled for a short time in nitric or sulphuric 

 acid and well washed in warm and cold water, then dried, 

 soaked in turpentine, and mounted in Canada balsam, as 

 usual ; or they may be mounted dry. 



Fig. 108. Spicula of Gorgonise : mixed Species, x 100. 



The spicula of the Gorgonia, or, as they are popularly 

 called, Sea-fans, are beautiful objects when seen under the 

 parabolic reflector, from which this drawing is taken. The 

 spicula are found imbedded in the body of the animal. There 

 are many species, three or four of which are British. 



The method of preparation is to boil the animal, or a por- 

 tion of it, in diluted potassa fusa until the mass breaks up by 

 tiie action of the fluid on the horny matter, when the deposit 

 may be removed and re-boiled for a short time in some fresh 

 potassa ; then well wash in warm and cold water, dry, soak in 

 turpentine, and mount in balsam. They may also be mounted 

 in a dry opaque cell. 



