T6 THE AMERICAN MONTHLY [April, 



taining nitric acid, and the usual materials and apparatus for mounting in 

 balsam, are all the appliances 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 an}- pertaining to the species in hand. This precaution 

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

 on accovmt 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 neighboring 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 young sponges, grown under 

 observation, from isolated statoblasts, whose identity has been satisfactorily 

 determined. 



Next, separate from the sponge some minute fragments containing skele- 

 ton spicules, the dermal and interstitial tissues, and a dozen or more gem- 

 mules. Place several of the last named, with a few adherent skeleton spi- 

 cules, 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 partiallv 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 w^ell, 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 accomplished 

 that the gemmules will absorb benzole freely and receive their covering of 

 benzole or chloroform balsam xyithout cloudings ^'PPb' the balsam and a 

 cover glass. This process of removing moisture by the use of alcohol, 

 rather than by drying 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 transparent 

 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 obtained by moimting some of the contents 

 of the test-tube. If the lately suspended spicules have now settled, carefully 

 pour ofi' 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. I have found it best to 

 allow the water to evaporate from these slowly, as, if hurried over a lamp, 

 each spicule is often margined with minute globules that it is impossible 

 afterward to remove. However, when the «lide is apparently quite dry, it 



