84 Mr. H. J. Carter on the 



tion in water, while the remnants of the crust themselves 

 continue to float with the greatest pertinacity. Still, although 

 in most instances where the statoblast is fully developed it 

 forms a thick coat, yet in others it can hardly be traced even 

 under the microscope after the fully developed statoblast has 

 been mounted in balsam ; while it must not be forgotten that, 

 as its development is progressive, it may be as wwtraceable at 

 an early period in one as in the other. 



Lastly, there is often a distinct layer of spicules which are 

 more like those of the skeleton than those of the statoblast, but 

 sufficiently differentiated by their peculiarities from both to 

 show that they do not belong to either (PL VI. fig. 8, Z, n) ; 

 and these form a very distinct capsular covering to the stato- 

 blast, in which probably it was originally developed, and thus 

 separated from its neiglibours. 



Generally the statoblasts are situated towards the base or 

 first-formed portions of the Spongilla, either fixed to the object 

 on which the sponge may be growing, or more or less scat- 

 tered throughout its structure. The details of their development 

 may be found in the papers to which 1 have last alluded; while, 

 as this is also progressive, they often present themselves in a 

 collapsed hemispherical state, without the crust, wlien the chiti- 

 nous coat, being uncovered, gives them an amber colour, and 

 thus their appearance generally is that of a different kind; but, as 

 before stated, the statoblast when fully developed is, especially in 

 the fresh state, globular, and, in proportion to the thickness of 

 the crust, more or less white in colour. Yet there is a crustless 

 spherical form, wherein too the aperture may be multiplicate — 

 that is, double, triple, or even quintuple (PI. V.fig. 5,ccc cc) 

 — as first noticed in another species by Gervais (No. 7) ; with 

 which also there appear to have been statoblasts that contained 

 two or three others of the same kind presenting the same 

 structure, the same composition, and the same yellowish colour 

 (apud Johnston, No. 10, p. 154) ; so that, as before stated, the 

 statoblast, although generally globular or elliptical, may have 

 these forms modified in a variety of ways, as indeed may be 

 seen in those which I have figured in Plates V. and VI. 



Now, as the statoblast has so far been found in nearly all 

 the freshwater sponges that have been described_, and never in 

 the marine ones, while the form of the skeleton-spicule is not 

 only always acerate but almost always more or less alike in all,it 

 follows from the latter being of little or no specific value that 

 the statoblast, which is difi'erent in all, at least in the form of 

 its spicules, must become the basis of the most reliable classi- 

 fication ; and therefore I shall use its characters for what in 

 this respect I may hereafter have to propose. 



