On the Development of the Freshivater Sponges. 4-03 



slenderer, and less curved than the English specimen. It has a 

 ventral siphimcle like the Beleinnite, and is supposed to have 

 been attached to a style more than G inches in length, like the 

 appendix to the pen of many Calaniaries. 



The plate ilhistrating Conuteuthis is wanting in most copies 

 of the ' Paleontologie Fran^aise,' but occurs in the ' Mollusques 

 Vivans et Fossiles ' of the same author, and one of the figures is 

 copied in my Manual, pi. 2. f. 9. 



XXXVIII. — On the Development of the Freshwater Sponges. 



By N. LlEBERKLHN*. 



The structures hitherto recognized as belonging to the fresh- 

 water Sponges are the following: — The skeleton, consisting of 

 siliceous needles of various forms ; the gelatinous substance ; 

 the so-called gcmmules, which are furnished with a pore, and 

 are either surrounded by a smooth shell, or by a ring of amphi- 

 disksf; moveable bodies occurring at certain periods of the 

 year, and effecting the propagation of the sponges : according 

 to Hogg, these move by an endosmotic process; according to 

 Laurent, by cilia. Grant has described similar bodies in the 

 marine sponges, ciliated in front, but not behind; Quekett was 

 unable to confirm this observation, and gives a totally different 

 account of the propagation. Huxley has described spermatozoa 

 in Tethya, and Carter in Spongilla. 



The following observations have been made almost exclusively 

 upon specimens of Spongilla fluviatilis, which I examined almost 

 daily in the fresh state during two summers and a winter. They 

 are very common in the river Spree at Berlin, especially upon 

 old wooden posts, and at the bottom of the water. 



Skeleton and Gelatinous Substance. — The siliceous spicula have 

 been frequently described, both in their common and unusual 

 forms (see Dujardiu's work upon the Infusoria, and Ehren- 

 berg's ' Mikrogeologie'). Meyen states that their ends are 

 connected together by a delicate colovu'less siliceous mass. I 

 have found this formation, especially in dead sponges, upon 

 which however gcmmules and young sponges are often situated ; 

 but the connecting material is not silica, for it is destroyed by a 

 red heat, the needles and amphidisks being left. The needles 

 are usually so arranged that several form a rod, the apex of 

 which is applied to the apex of similar rods at an obtuse angle. 



* From Mullet's Archiv, 185fi, i. 



t The term Amphidiscus was ap])lied by Ehrenberg to a supposed genus 

 of Infusoria, consisting of bacillar spicules of sponges with discoidal ends. 

 —Ed. 



26* 



