MEMOIRS. 



Some Account of Kleinenberg's Researches on the 

 Anatomy and Development of Hydra. By Professor 

 Allman, M.D.,LL.D., F.R.C.S.I., F.R.S., M.R.I.A. 



Since Abraham Trembley about a hundred and thirty years 

 ago first made us acquainted with some of the most important 

 facts in the morphology and vital phenomena of Hydra, this 

 remarkable little animal, which, along with Cordylophora, 

 constitutes all we as yet know of the hydroid fauna of the 

 fresh waters of our globe, had become the subject of various 

 investigations. Many of these, however, had led to results 

 manifestly erroneous, while even the most careful and com- 

 plete of them had left much to be still determined regarding 

 the anatomy, development, and life-history of an animal whose 

 examination by Trembley marked out one of the great epochs 

 in the progress of biological research. 



Quite lately, howevei*, a memoir on Hydra^ has been pub- 

 lished by a German zoologist, Dr. Nicolaus Kleinenberg, 

 which, in exhaustiveness and in the value of the results 

 arrived at, must take its stand among the most important of 

 recent contributions to the zoology of the lower members of 

 the animal kingdom. It is proposed to give here a resume of 

 the most significant facts which the researches of Kleinenberg 

 have made known to us — researches which extend over the 

 fields of both anatomy and development. His observations 

 have been made chiefly on Hydra viridis, but they also 

 include the forms which he mentions under the names of 

 H. aurantiaca and H. grisea, and which are probably only 

 varieties of H. vulgaris. 



The anatomical section of the memoir embraces the struc- 

 ture of both endoderm and ectoderm — tissues which differ in 

 some very important points from one another. 



The endoderm is composed entirely of cells, which are 

 arranged in a single layer. These cells are simjile nucleated 



^ ' Hydra, eine Anatomisck-entwicklungsgescbichtliclie Uutersuchung.' 

 Von Dr. Nicolaus Kleiuenberg, Mit vier lithograpliirten Tafeln. Leipzig, 

 1872. 



VOL. XIV. NEW SER. A 



