232 FOURTH REPORT 1834. 



addition to his treatise on the Entozoa of the human species, has 

 published a series of plates intended to illustrate Rudolphi's ge- 

 nera, in which, by engraving on a dark ground, the white and 

 transparent parts of these animals are brought out in an admirable 

 manner. Van Lidth de Jeude has also published more recently 

 (1829) a collection of lithographed plates of these animals*. 



3. Acalepha. — Our knowledge of this class must be considered 

 as very imperfect, notwithstanding it has engaged the attention of 

 many excellent observers. This is in a great measure to be at- 

 tributed to several difficulties connected with the study of these 

 animals, particularly those arising from their very delicate struc- 

 ture, which renders the preservation of specimens in many cases 

 almost impossible. Peron and Lesueur published some valuable 

 memoirs on the Medusa: (taking this term in its full extent) in 

 the 14th and 15th volumes of the Ann. du Mus., which contained 

 a far more detailed history of this tribe than any that had ap- 

 peared before, and contributed greatly towards an improved clas- 

 sification of it. These authors are, however, generally allowed to 

 have overmultiplied the species, and to have established several 

 genera upon insufficient observation. Many additions to this 

 class, and to our knowledge of its structure, were made subse- 

 quently by Chamisso and Eisenhardt m the 10th volume of the 

 Nova Acta Sfc. A^at. Ctir., and a few in the 11th volume of the 

 same Transactions by Otto. Quoy and Gaimard also collected 

 much information with respect to the habits and organization of 

 these animals during their voyage with Freycinet. Some of their 

 observations were published in the An7i. des Set. for 1824t and 

 1825J. In this last volume, their remarks, so far as the Aca- 

 lepha are concerned, relate only to the genus Beroe. In the 

 BicU. de la Soc. Phil, for 1824§, M. De Freminville has pub- 

 lished some observations on the Physaliajjelagica, to which are 

 annexed descriptions of three new species belonging to that ge- 

 nus. Some researches on the structure of the Physalice were 

 published about the same time in the 9th volume of the Peters- 

 burgh Memoirs by Eichwald. In 1825, Rosenthal published 

 some collections towards the anatomy of the Medicsce\\, the spe- 

 cies principally examined being the M. aurita, Linn. In 1827, 

 another memoir was published by Quoy and Gaimard in the 

 Ann. des Sci.%, containing an account of a vast number of new 



• Besides the above works, I may mention that of Nordmann, already alluded 

 to, from which some valuable extracts will be found in the Ann, des Sci. Nat. 

 for 1833, torn. xxx. 



t tom. i. p. 2 15 X torn. vi. p. 28. § p. 42. 



II Bull, des Sci. Nat. (1826), tom. ix. p. 253. ^ tom. x. 



