170 PROCEEDINGS OF THE ACADEMY OF. [1887. 



follow: the normal sponge, the dermal film, the transparent 

 gemmule, and a display of the detached spicules. Neither would 

 alone answer, but the series will settle all points, excepting in the 

 case of the genus Carterius. When this is suspected, the gemmules 

 should first be examined dry; and, in preparations for mounting, 

 great care should be taken to avoid the destruction of the tendrils, 

 (cirri) (PI. VI, figs, iii, iv, v. and vi), by the prolonged use of strong 

 acid. Expert microscopists will improve their gemmule mounts by 

 dividing some of them with a thin knife, endeavoring to make the 

 section through the foraminal aperture; this, in the case of species 

 having long birotulates, such as Meyenia crateriforinis, (PL V, fig. 

 vi,), is of the utmost importance. 



"Seniors" in microscopy will please pardon the minutiae of the 

 processes just given, as they were necessary to make them available 

 for the "freshmen." All are reminded that the above directions as 

 to collection and examination refer to mature sponges only. It is 

 seldom safe, or even possible, to name one, in which no gemmules 

 can be found. If a course of study is undertaken, involving the 

 histology and physiology of fresh-water sponges, many peculiarities 

 will of course be observed that have not been alluded to here. One 

 ofthem concerns the development of the spicules and, if not understood, 

 will pretty certainly mislead the beginner into the supposition that 

 he is examing a novel species. Both the skeleton and dermal 

 spicules of young sponges are frequently marked with bulbous 

 enlargements at the middle and often half way between the middle 

 and each end of the spicule. These seem to indicate an imnuitu're 

 condition, as they disappear when the spicules are fully formed. 



A few words may be needed to justify the specific groupings I 

 have adopted. I am well aware that objections may be made to so 

 large a use of Avhat some will call a "trinomial nomenclature." 

 Without expressing an opinion as to the policy of the practice as 

 regards other branches of the animal kingdom, in the case of the 

 sponges I think it clearly unavoidable; for the reason, that tlie 

 inert parts that have just been described as typical, share with the 

 vital amoeboid cells, their well known characteristic of unlimited 

 variability. Were all the names that have been dropped or marked 

 as varieties to be recognized as full species, on the ground 

 that the specimens so designated do not exactly resemble any others, 

 the literature would be encumbered with a mass of names represent- 



