ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 309 



needed. As the processes to be described are certain to disturb the 

 normal relations of the several classes of spicules to each other, it is well 

 before the dried specimen has been much handled, to separate some clean 

 portions of the outer or dermal film ; lay them upon a slide and mount 

 in balsam without further preparation. An examination of this may 

 determine the presence and decide the character of the dermal spicules, 

 if there are any pertaining to the species in hand. This precaution is 

 necessary in view of the displacement of parts just mentioned, and also 

 on account of the indiscriminating habit of the sponge-currents during 

 life, which almost necessarily charge the tissues with various foreign 

 particles, including vagrant spicules of its own and neighbouring species. 

 In practice, the rightful presence of dermal spicules in any species is 

 often so doubtful, that it can only be settled by an examination of youn<» 

 sponges, grown under observation from isolated statoblasts, whose identity 

 has been satisfactorily determined. 



Next, separate from the sponge some minute fragments containing 

 skeleton spicules, the dermal and interstitial tissues, and a dozen or more 

 gemmules. Place several of the last-named with a few adherent skeleton 

 spicules upon the centre of a fresh slide ; bring to the boiling-point in 

 one of the test-tubes five or six drops of nitric acid, and by the aid of a 

 dropping-tube apply a single drop of the hot acid to the gemmules 

 upon the slide. While the acid is partially destroying their cellular or 

 granular crust, pour the remaining 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 the 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 minutes that have elapsed will probably have been as 

 much as the gemmules 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 

 practice, to boil 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 off all the water that can be reached and apply repeated drops of 

 strong alcohol to take up the remainder. When this is so far accom- 

 plished that the gemmules will absorb benzole freely and receive their 

 covering of benzole and chloroform balsam without clouding, apply the 

 balsam and a cover-glass. This process of removing moisture by the 

 use of alcohol, rather than by drying over a lamp, is to be 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 ; but a better view of the detached spicules is necessary, and 

 may be obtained by mounting some of the contents of the test-tubo. 

 If the lately suspended spicules have now settled, carefully pour off all 

 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. It is best to allow the water 



