412 On the Development of the Freshwater Sponges. 



which spouges grow. Their microscopic constituents are, — 

 germ-granules of the above-described form and size, which con- 

 tain either a finely granular globule distinctly contrasted with 

 the enclosing shell, or a cell-like body containing a low refracting 

 body resembling the nucleolus of the sponge-cells ; germ-gra- 

 nules, which protrude a sarcoid substance from some part of their 

 surface, and this is continued within the germ-granule, the outline 

 of the portion situated outside being continuous with that lying 

 within ; large and small ordinary sponge-cells, some containing 

 a distinct nucleolus, whilst others merely form an aggregation of 

 fine granules and sarcoid substance, exhibiting the Amoeba-like 

 movement ; variously formed small and large siliceous needles, 

 some resembling the smooth and tuberculated forms met with 

 within the swarm-spores and the aggregations of germ -granules, 

 others being larger, but not so large as the fully developed ones. 

 It is uncertain whether these spicula are developed from the 

 germ-granules ; some of them agree in size with these ; they 

 are either spherical, drawn out into fine points at the ends, or 

 spindle-shaped, and usually tubercular ; they are easily recog- 

 nized by the refractive power peculiar to siliceous spicula, but in 

 the smallest specimens even tbis character becomes uncertain. 

 Whether the above-described reproductive bodies of sponges are 

 the only ones which occur, or whether sponge-cells also propagate 

 by spontaneous division, is unknown. 



A comparison of Sponges with allied bodies may be met with 

 in J. Miiller's memoir upon Thalassicolla, Collosphara, and 

 Acanthometra^- . 



The Spermatozoa-like bodies. — In June of the last and the 

 present years, large numbers of moving corpuscles were not 

 unfrequently seen on dissecting sponges, which were readily 

 distinguishable from those giving rise to the movements of the 

 swarm-spores ; for in the former the filament is much longer 

 and thicker, and the head much smaller. When swarming, their 

 heads are usually directed towards each other, and their move- 

 ments greatly resemble those of ordinary spermatozoa. They are 

 seldom met with in the locality where they are developed. They 

 are formed in globules enveloped by a transparent structureless 

 membrane, and surrounded by sponge-cells. The globules are 

 about ^iy inch in diameter. They are seen to move to and fro 

 within the globules until these burst, when they swim away in 

 large or small groups, the filament constantly vibrating to and 

 fro. To determine their import as spermatozoa, I endeavoured 

 to observe their entrance into the pore of the gemmule, as per- 

 haps forming the micropylc, but in vain. 



* Monatsbcricht tier Kerliner Akiulemie, April 1H;"),5. 



