78 THE BIOLOGY OF THE ANIMAX 



suit ? Compare with the same experiment on 

 the spicules of Spongilla. What difference? 

 Of what are the spicules of Grantia composed ? 

 5. The histological structure. — Good results can 

 usually be obtained only from material which 

 has been stained — e. g., in Delafield's hgematoxy- 

 lin, eosin, or borax carmine — embedded in cel- 

 loidin or paraffine, and sectioned preferably on 

 a microtome. If such sections can be obtained, 

 the more minute structure of the sponge may 

 be studied under the high power. It will then 

 be seen that the sponge flesh or syncytium, 

 which fills all the space among the radial 

 canals and in which the spicules are embed- 

 ded, is made up of granular protoplasm in 

 which many nuclei are prominent. Sometimes 

 the outlines of the constituent cells may be dis- 

 tinguished. The radial canals are lined with a 

 layer of cells which form the endoderm. Pos- 

 sibly, in well-prepared specimens, each cell of 

 the endoderm may be seen to have a single 

 long cilium or flagellum. In places may be 

 found dark -colored oval or spherical masses, 

 eggs or embryos, lying in the syncytium just 

 below the endoderm. 



An excellent method of obtaining isolated sponge cells 

 for microscopic examination is to put living sponges, as 

 Grantia, Ohalinula, etc., into a dish of sea water, quiet- 

 ly remove nearly all of the water with a pipette, then 

 quickly pour over them a saturated solution of corrosive 

 subhmate. After a moment the water in the neighbor- 

 hood of the sponge, especially if carefully agitated, will 

 become milky. Put some of this cloudy water on the 



