On the Development of the Freshwater Sponges. 403 



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

 ventral siphuncle like the Belemnite, and is supposed to have 

 been attached to a style more than 6 inches in length, like the 

 appendix to the pen of many Calamaries. 



The plate illustrating Conoteuthis is wanting in most copies 

 of the ^ Paleontologie Frangaise/ but occurs in the 'MoUusques 

 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. LlEBERKUHN*. 



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 gemmules, 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 Dujardin's work upon the Infusoria, and Ehren- 

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

 connected together by a delicate colourless siliceous mass. I 

 have found this formation, especially in dead sponges, upon 

 which however gemmules 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 Miiller's Archiv, 1856, i. 



t The terra Amphidiscus was applied by Ehrenberg to a supposed genus 

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

 —Ed. 



26* 



