26 PEACTICAL PAEASITOLOGY 



termed " pansporoblasts." They correspond to the sporonts of 

 Pleistophora and Thelohania, and, after repeated division of the 

 nucleus, they break up into a varying number of cnidospores. The 

 cnidospores are at first uni-nucleate but, by repeated division, the 

 nucleus becomes fourfold. Of these four nuclei, one 

 forms the nematocyst and another the shell, while the 

 other two form the amoeboid germ, which, later, 

 emerges from the shell. The manner in which fer- 

 tilization takes place is not exactly known, but it is 

 probable that, as in the Amoebae, it is by autogamy. 

 In older cysts the protoplasm is reduced to a thin wall, 

 the whole of the interior being occupied by a hollow 

 FIG. 3. Cnido- s P ace filled with cnidospores. 



spore of Glugea In place of Glugea anomala, an example of a 



gTTn/m a t /c" Microsporide which forms large cysts is furnished by 

 (After stempeii.) Glugea lophii, Dofl. This parasite inhabits the axis- 

 5 oof: 1 !.) a cylinder processes of the ganglion cells of Lophius 



piscatorius, which is fairly common in the Mediter- 

 ranean, and may be obtained from one of the zoological stations in 

 that neighbourhood. 



Order 2. Myxosporidia. 



The Myxosporides are distinguished by certain structural peculiari- 

 ties of the cnidospores. These are formed in pairs within a pansporo- 

 blast ; they are enclosed in a bivalve shell ; and their nematocysts 

 two or, more rarely, four in number are projected in response to very 

 slight stimulus. In the case of a few very minute varieties, found in 

 the gall-bladder of fish, the entire organism forms a single pansporo- 

 blast which dies after the formation of the cnidospores. The large 

 majority of the Myxosporides, however, appear as plasmic bodies of so 

 large a size as to be almost visible to the naked eye. The interior of 

 these bodies, like that of the microsporide, Glugea, is filled with 

 numerous pansporoblasts which are definitely separated from the 

 surrounding plasm. The Myxosporides are widely distributed among 

 fish and are found, though with less frequency, among other cold- 

 blooded animals. They occur either in the hollow organs (gall-bladder, 

 urinary bladder, uriniferous tubules), where they perform amoeboid 

 movements, or they occur as tissue parasites. 



(a) Myxidium lieberkiihni, Biitschli. 



Of those varieties of Myxosporides which inhabit the hollow organs 

 and are capable of amoeboid movement, the most readily obtainable 

 is Myxidium lieberkiihni. It occurs, sometimes in very large numbers, 



