2IO 



THE AMERICAN MONTHLY 



[November, 



minute germinal matter, consisting of 

 transparent germs of different sizes, 

 the whole enclosed by a delicate in- 

 vesting membrane, slightly protruding 

 at the aperture, and presenting a re- 

 ticulated appearance like that of vege- 

 table cell structure. Next comes a 

 comparatively thick, chitinous mem- 

 brane, of an amber color, which, when 

 viewed in the whole statoblast, has a 

 deeper color than when separated. 

 Then cumes another coating or ciust 

 which, in two instances, is com- 

 posed of cell structure, hexagonal in 

 section, but in the rest of a white 

 granular or micro-cellular substance, 

 which can only be seen by a very 

 high-power object-glass. It appears 

 to afford a floating property, like cork, 

 to the statoblast, and varies much in 

 thickness according to the species. 

 Its composition is still, I believe, a 

 disputed point, Meyen thinking it was 

 lime, having a cellular formation, but 

 in no case has it been known to effer- 

 vesce when brought into contact with 

 hot or cold acids. This crust is 

 charged or accompanied by spicules 

 of different forms, variously arranged 

 according to the species, and on which 

 the classification of the fresh-water 

 sponges is now founded. 



Although the statoblasts have been 

 known so many years, Johnston, in 

 his description of the British species, 

 does not mention the presence of 

 spicules except in a foot-note, stating 

 that Meyen, in 1839, discovered bi- 

 rotulate spicules, and others with 

 minute spines on their surface, evi- 

 dently believing, at that time, that the 

 two belonged to the one species of 

 sponge; perhaps a natural conclusion 

 to have come to then, as -the two were, 

 and are often, found growing together 

 in the same locality, and the micro- 

 scopical appliances for seeing them 

 were not then anything like so perfect 

 as they are now. In some species, as 

 in llibclla reticulata, the statoblast is 

 enclosed in a distinct layer of spicules, 

 which partake more of the character 

 of the skeleton spicules of the sponge. 



forming a capsular covering, in which 

 it was probably developed. 



We will now pass on to the classifi- 

 cation of the fresh-water sponges, as 

 founded by Mr. Carter on the form 

 and structure of the statoblasts, as far 

 as present known, omitting for brevity 

 the general structure of the sponge, as 

 I mentioned at the commencement of 

 this paper. 



The first genus comprises the Spon- 

 gilla, containing ten species, whose 

 statoblasts are globular, crust thick 

 or thin, and in some cases absent 

 altogether, accompanied by minute 

 acerate spicules, smoothed or spined 

 according to species. 



In Spongilla Carter i the spicules are 

 smoothly acerate, and the crust is 

 composed of pyramidal columns of 

 dodecahedral or polyhedral cells, 

 hexagonal as seen in section or when 

 focussing for the surface, regularly ar- 

 ranged one above another in juxtapo- 

 sition, perpendicularly to the outside 

 of the chitinous coat. This species 

 has only been found as yet in India, 

 Mauritius, and lately by Dr. Margo of 

 Buda Pest, in Europe, in the lake of 

 Balaton. My own specimen, for which 

 I am indebted to Dr. Matthews, comes 

 from Jheels, opposite Benares. The 

 only British species of this genus is 

 SpiVigiUa hicustris, the statoblasts of 

 which have the spicules more or less 

 curved, minute, stout and sharp- 

 pointed. They are covered with stout, 

 recurved spines, the outer crust being 

 composed of micro-cellular structure. 

 This species is found growing some- 

 what plentifully up the Thames, at 

 Henley, Goring, and Marlow, and is 

 also met with in Europe generally, 

 North America, and Asia, but the 

 finest specimens that I have seen have 

 come from the Upper Thames. 



The remaining eight species of this 

 genus are .5". alba, S. paiipcrenta, S. 

 ciiii'rea, S. cerebe/latd, S. navkella, S. 

 viiiltiforis (so named on account of 

 ha\'ing several openings to the stato- 

 blast ; this species is also apparently 

 devoid of a crust), S. Lordii and S. 



