238 Miscellaneous. 



nature are described by Lieberkiihn in his recent memoir on the 

 SponffiUce. 



The parenchyma of the body of the Spongillee presents a very 

 variable arrangement, whilst the siliceous skeleton retains the same 

 characteristic form in all specimens. Sometimes the parenchyma 

 exhibits a cavernous structure, containing cavities more or less iso- 

 lated from each other, and connected either with the orifices of 

 ingestion or with tubes of ejection ; sometimes these cavities are 

 replaced by a system of canals extending through a great portion of 

 the Sponge, and opening directly into the tube of ejection ; in this 

 case a great part of the integument is destitute of orifices of in- 

 gestion. In other cases the cutaneous pores are dispersed in great 

 numbers over the whole surface of the Sponge, and usually lead into 

 a large cavity belonging to the system of ingestion. The walls of 

 the partitions bounding these cavities bear vibratile apparatus. In 

 other Spongillce there do not exist membranous partitions bounding 

 the cavities ; but the body is traversed in all directions by trabeculee 

 of diflPerent thicknesses, which are often supported upon the integu- 

 ment. Some of these are completely smooth in appearance, and 

 show no appreciable outlines of cells ; the strongest bear vibratile 

 apparatus : others are constricted like a necklace, being formed of a 

 simple series of cells in juxtaposition. Others, again, are composed 

 of several rows of cells, of which the limits are visible only at the 

 surface (so as to resemble an epithelial coat) or only at the centre of 

 the trabecula. 



All these different appearances may be presented successively by 

 one and the same Spongilla. Homogeneous parenchymatous parti- 

 tions have contracted, under the eyes of M. Lieberkiihn, into trabe- 

 culee with a cellular structure and of a necklace-like form. On the 

 other hand, he has seen neighbouring trabeculee spread out and be- 

 come united in such a manner as to form a membranous wall. The 

 cavities open into one another, and separate again. Fragments of 

 Spongillce artificially detached prove that the cells of the parenchyma 

 can unite in a few hours to form a cutaneous envelope. 



The pores of ingestion are not characteristic of the integument, as 

 perfectly similar orifices are seen to originate in the membranous 

 partitions of the interior of the body. The tubes of ejection are the 

 seat of very peculiar movements. The author has seen the cells of the 

 innermost layer gliding up the wall of the tube, and again descending. 



M. Lieberkuhn has positively demonstrated a fact which has only 

 been suspected since the observations of Laurent — namely, the re- 

 production of Sponges by spontaneous division. In individuals kept 

 in vessels filled with spring water he has seen the body contract, 

 and emit here and there processes, which soon became detached and 

 glided over the vacant portions of the siliceous skeleton, and even 

 upon the bottom of the vessel. This division appears only to take 

 place in individuals which are nearly perishing. But the fragments 

 thus set free continue to live, and in the course of a few weeks they 

 have produced in their interior sihceous spicules and vibratile ciHa. 



In these fragments of Spongilla, and in perfect individuals in a 

 dying state, M. Lieberkiihn has witnessed phenomena which might 



