728 OKDER: MYXOSPORIDIIDA 



Gemis : Henneguy a Thelohan, 1892. 

 Spores more or less globular or ovoidal. Two polar capsules at the 

 anterior end. Posterior end of the shell valves prolonged into more or 

 less extended processes, which unite and form a tail in the median line. 

 Thirty-two species. Polysporous, disporous, and monosporous. Twenty- 

 eight species in tissue and four in body cavity. In fresh- water fish, except 

 one. Type species: Henneguya psorospermica Thelohan. 



Genus: Hoferellus Berg, 1898. 

 Spores pyramidal, with two posterior processes from the lateral faces. 

 One species. Polysporous. Tissue and body cavity of fresh-water fish. 

 Type and only species: Hoferellus cyprini Doflein. 



DETAILED DESCRIPTION OF CERTAIN SPECIES. 



Myxobolus pfeifferi Thelohan, 1894. — This organism is a common 

 parasite of the barbel, Barhus fluviatilis. It infests all the tissues of the 

 body, including the skin and gills, on which it gives rise to nodules and 

 tumours, which may be of large dimensions. In the infected tissues the 

 Plasmodia are closely intermingled with the host cells, so that often there 

 is difficulty in defining the limits of the parasite. The infected area of 

 tissue is frequently enclosed by a fibrous capsule formed by the host, and 

 in this the parasite in the form of a multinucleate plasmodium continues 

 its development (Fig. 305). Spores are continuously being formed in the 

 cytoplasm of the parasite. Eventually the parasite dies, and all that 

 remains is a fibrous nodule which, on section, is seen to contain many 

 spores in the interstices of the tissue. Spore formation has been studied by 

 Keysselitz (1908). In the plasmodium, one of the nuclei becomes separated 

 with some cytoplasm as a cell, which Keysselitz calls the propagative cell 

 (Fig. 308). After unequal nuclear division a large and small cell are 

 produced. • Two such couples become associated, and the aggregation of 

 the two large and two small cells proceeds to the development of two 

 spores. The two small cells spread over the surface of the two large cells 

 to form an envelope, while the nuclei of the two large cells multiply till a 

 total of twelve are present. The cytoplasm of the two large cells may now 

 unite. Of the twelve nuclei, four, which are gamete nuclei, become 

 centrally placed, while eight take up a peripheral position. If the cyto- 

 plasm has united division takes place, so that two bodies are produced, 

 each with two centrally placed gamete nuclei and four peripheral nuclei. 

 Each of these cells with six nuclei develops into a spore. Two of the 

 peripheral nuclei form the two valves of the spore, while two give rise to 



