1887.] NATURAL SCIENCES OF PHILADELPHIA. 169 



fragments into the acid left in the test tube and boil violently, until 

 all the tissues are destroyed and the spicules left as a sediment upon 

 tlie bottom of the tube. Fill up the tube with water and stand it 

 aside to settle ; which may take an hour or more. The few min- 

 utes that have elapsed will probably have been as much as the gem- 

 mules upon the slide will bear : they must not be left so long as 

 to destroy the chitinous coat, nor is it well, though a common prac- 

 tice, to hoil them upon the slide for this often smears and disfigures 

 it with frothy matter. Remove most of the acid by trickling drop 

 after drop of water over the slide while held in a slightly inclined 

 position. Wipe ofl[ all the water that can be reached and apply re- 

 peated drops of strong alcohol to take up the remainder. When 

 this is so far accomplished that the gemmules will absorb benzole 

 freely and receive their covering of benzole or chloroform balsam 

 without clouding, apply the balsam and a cover glass. This pro- 

 cess of removing moisture by the use of alcohol, rather than by dry- 

 ing over a lamp, is preferred, although it requires more care and 

 time, because the gemmules are less likely to be distorted in shape 

 and the cells of the crust to become filled with air, if they are kept 

 always under fluid. Yet if the mounted gemmules, when examined, 

 appear black, showing an accidental intrusion of air, much of this 

 can be removed by carefully heating the slide over a lamp. 



If this mount has been successful, the gemmules are now so trans- 

 parent that their surrounding spicules can be readily seen and the 

 genus determined, by the aid of the "Key" hereafter given ; but a 

 better view of the detached spicules is necessary, and may be ob- 

 tained by mounting some of the contents of the test-tube. If the 

 lately suspended spicules have now settled, carefully pour ofiTall the 

 water except one or two drops ; though if there has been much acid 

 used it may be better to wash them a second time. Shake up and 

 place a sufficient quantity upon one or more slides, being careful 

 not to leave the contained spicules in too dense a mass. I have 

 found it best to allow the water to evaporate from these slowly ; 

 as, if hurried over a lamp, each spicule is often mai'gined with min- 

 ute globules that it is impossible afterward to remove. However, 

 when the slide is apparently quite dry, it may be safely exposed a 

 moment to the heat, to make sure of it, and then covered with bal- 

 sam and glass as usual. 



The investigator has now before him all the elements necessary 

 for solving his specific jiroblem, according to the formuhe Avhich 



12 



