274 Transactions of the Society. 



filled with email spherical cells of uniform size, pi. VI. figs. 13 and 

 13a. The spherical bodies are probably a stage in the development 

 of the elongated bodies. The real nature of these parasites, which 

 probably belong to the class known as Sporozoa, their development 

 and mode of entry, remain obscure ; they have no motion of their 

 own, but float in the fluid of the body-cavity on which they live 

 and are continuously shifted about by the contraction of the roti- 

 fer's muscles. The Synchaetae do not seem to be much incon- 

 venienced by the parasites, but no doubt they succumb eventually. 

 These parasitic protozoa are evidently the same which Dr. Bertram 

 has described as '* Parasitische Schlauche in der Leibeshohle von 

 Eotatorien,"* and which he found in some Brachionus pala. They 

 have also been mentioned by Dr. Zacharias as occurring in Syn- 

 chaeta and named by him Ascosporiduim blochmanni ; f and Prof. 

 A. Fritsch has described similar parasites under the name of 

 Ghigea asperospora. \ The parasites lately described by Mr. A. M. 

 Przesmycki § as occurring in Brachionus are of a different nature ; 

 the latter are very much smaller unicellular cells which render 

 Brachionus and other rotifers quite white and milky. 



The Synchaetae occur both in fresh and brackish water and in 

 the open sea, but it seems to me that they keep to their respective 

 elements and that the fresh-water species are never found in salt 

 water, and the salt-water species never in fresh water. If a & 

 pectinata be placed in brackish or sea water it dies in a few minutes, 

 and if the marine S. triophthalma be placed in fresh water the same 

 thing occurs. It cannot be supposed that salt water or fresh pond 

 water can exert a poisonous influence on these species respectively. 

 The inability of these rotifers to live in an element to which they 

 are not accustomed" is due to the mechanical action of fluids having 

 different densities on the cell-contents of their tissues and organs. 

 The specific gravity of fresh water being 1, that of sea water is 

 1'027, and this is quite sufficient to produce strong diffusion 

 currents by osmosis between the outside fluid and that contained 

 in the body-cavity, and eventually in the cells of the various 

 organs. The lighter fluid will get through the cell-walls quicker 

 than the denser fluid can get out and vice versa, with the result that 

 the cells and the whole animal will either swell or shrivel up, and 

 this w r ill injure or burst the delicate cells and completely stop the 

 functions of the various organs, causing the death of the animal. 



As regards their appearance, some forms such as S. pectinata, 

 tremula, and oblonga can be found all the year round, but often 

 appear in greatest numbers in the winter months or very early 



* Zool. Jalirbiicher, Bd. v. 1892, pp. 596-600. 



t Ploner Forschungsbericbte, Teil 6, 1898, p. 48. 



% Ueber Parasiten bei Crustaceen und R'aderthieren der siissen Gew'asser. Bull. 

 Intern, de l'Acad^niie des Sciences de l'Empereur Frarjc.ois Joseph I., Prague, 1895. 



§ Ueber Parasitische Protozoen aus dem Innern der Rotatorieu. Bull, de 

 l'Acade'mie des Sciences de Cracovie, 1891. 



