FEERIIWATEE SrONGES. 87 



which become lurther protccled by 11 rm cellular crusts in which is embedded, iu deuse 

 aud orderly array, a third class of very peculiar and distiuctive siliceous spicules. These 

 are of two typos, the siiined Monaxou and the birotulate Mouaxon. The "seedlike" 

 capsular bodies are variable iu size, averaiiiuy al)Out the one-fittieih ot an inch iu 

 diameter. There is a small round aperture iu the capsule communicating M-^ith the 

 central cavity. The aperture has generally a short tubular extension outwards aud is 

 called the " foramen." The internal cavity is filled with a cellular protoplasmic matter 

 which comes out next spring with an amoeboid movement, and develops into a new 

 sponge. These well-protected capsules of germinal plasm have been called by various 

 names, such as " ovaria," " statoblasts," " statospheres," or " gemmiiles." The statoblasts 

 are foixnd often in layers near the base of the sponge, sometimes scattered, or in loose 

 clusters, or in minute, compact, spherical aggregations throughout the sarcode. The 

 character of the spiculation of the staloblast forms the artificial basis of our genera as 

 originally determined by Carter. 



Some of our sponges are thought to be perennial ; but there is no doubt that the 

 statoblast is the special agency for proiaagating the life of the fresh-water sponge lieyond 

 the generally lethal chill of Avinter. The Spongillida3 have been considered to be dis- 

 tinctly separated by this peculiarity from Ihe marine sponges, which, from their habitat, 

 are not so much affected by the annual variation of temperature. But their close phylo- 

 genetic allinity is strikingly suggested by the following observations. In the four species 

 of fresh water sponges (Lubomirskia) found by Dybowski so abundantly in Lake Baikal, 

 no statoblasts have as yet been discovered. Possibly, for anything Ave know as yet, the 

 marine habit may coexist in the deep Avaters of our oavu greater lakes. On the other 

 hand, capsular bodies, having a close resemblance to the statoblast, have been described in 

 three genera of the marine Silicispongiae, namely Chalina, Cliona, and Suberites. (M. E. 

 Topsent, Comptes Rendus, CV. 1888, pp. 1298-1300). The enclosing capsules in these 

 are, hoAvever, much more simple than those in the fresh-Avater sponges, as they are 

 Avantiug in the foramen, the massiA'e cellular crust and the siliceous armature. 



The position of the fresh-water sponges in Prof. Sollas's system of classification is as 

 follows : — 



The Phyllum.— SPOXCiil^ (Sponges). 



Branch B.— MICEOMASTICOEA. 



Class IL— ;S/i^ WISPOMiL E. 



Sub-Class ii. — Deniospoiigise. 



Tribe A. — Monaxonida. 



Order 1.— MONAXONA. 



Family 7. — Spongillid^ [Fresh-^water Sponges.) 



Proa'isional Conspectus 



OF 



Canadian Spongillid.e. 



Genus I. — Spongii.i.a. Statoblast spicules, one class of spined monaxons, tangential. 

 Species 1 . — Spoiigillafragilis. ") 



" 2.-SpongiUaMacKayi. \ A- Dermal spicules, absent. 



" 3. — Spongilla lacuHris. ) t^ , f acerates. 



" 4.-SpongiUa Terr^-Nor^c. \ ^"'"^^^ ^'P'^"'^'' ( birotulates. 



