Fresh-water Sjjonge. 163 



Keiehertj on the contractile substance and intimate structure 

 of the Campanularidae, Sertularidae and Hydridae^ translated 

 in the Annals and Magazine of Natural History for Jan. 1867, 

 from the Monatsbericht der Akademie der Wissenscliaften zu 

 Berlin^ July 1866^ p. 504; and for the Histology of the entire 

 sub-kingdom Coelenterata, see Kolliker, Icones Histiologicae 

 ii., Abtheilung, Hft.i., 1866, 



50. Fresh- WATER Sponge {Spongilla Lacustris), 



From the Isis, growing on the wall of a lock. 



This specimen, like the preceding, is plant-like in appearance, 

 consisting as it does of a root-like basis of attachment, and two 

 upright stems arising close together from it. The stems are about 

 five inches in height, and of the thickness of a drawing-pencil, but 

 the Spongilla Lacustris not rarely attains a greater size than this. 

 Owing to its having been preserved in spirit, this specimen has its 

 sm-face more fenestrated than it was in the living condition ; its 

 protrusible bladder-like cloacae are no longer visible ; and its eme- 

 rald-green colour is nearly lost. Its exterior is hispid with fascicles 

 of spicula, and the orifices in which the cloaeal oscula were lodged 

 are very plain ; though the smaller inhalant orifices or * pores^ 

 are not distinguishable, and indeed can only be seen in small 

 and transparent specimens under the microscope. Towards the 

 lower part of the stem, numbers of reddish globular seed-like 

 bodies, the asexual reproductive gemmae, formed towards the close 

 of the summer, are to be noted. The coriaceous capsule of these 

 gemmae is strengthened in this species, not by the birotulate 

 spicula kno^\Ti as 'amphidiscs' from their resemblance to a couple 

 of toothed wheels connected by an axle, and existing in the other 

 fresh- water Sponge, Spongilla Jliiviatilis, but by simple curved 

 acicular spicula which lie in it parallel to its surface. These 

 spicula are al>undantly spinous, as are also the spicula which 

 are to be found in the dermal membrane of this, though not of 

 the other fresh- water species ; the spicula of the skeleton proper 



M 2 



