320 THE SPOROZOA 



Schewiakoff found others attached in couples by their anterior extremities, 

 and then frequently showing peculiarities in their nuclei which led him 

 to suspect that conjugation may also take place between spores, but he 

 was unable to confirm the existence of any such process. The spores 

 are set free by bursting of the cysts and are to be found sticking to the 

 muscles, but their further development was not followed, and it is not 

 known how the Cyclops becomes infected with them. 



As regards the systematic position of these interesting parasites, 

 Schewiakoff thinks that " they should, without doubt, be placed amongst 

 the Sporozoa." If so, however, they differ from all known Sporozoa, first 

 in the possession of a contractile vacuole in the trophic stage, secondly 

 in their tendency to form plasmodia, and thirdly in the power of 

 multiplication by fission possessed by the spores. They have indeed a 

 certain superficial resemblance to the species of Thelohania which are 

 also parasitic on the muscles of Crustacea, but they differ from all 

 Myxosporidia in the simple, undifferentiated character of the spores, 

 a feature in which they resemble the Haplosporidia. If the Sporozoan 

 affinities of these parasites are, as they seem to be, undeniable, then they 

 must be regarded as quite the most primitive members of the group, 

 linking the Sporozoa in an unmistakable manner to the true Rhizopoda. 



The systematic enumeration of the Sporozoa would not be complete 

 without mention of the very numerous forms of supposed parasites 

 described from various human diseases. A list of these doubtful organisms, 

 with full bibliographical references, will be found in Lab be ([4] pp. 128- 

 132), under the title " Pseudo-coccidies," and a bibliography, complete up 

 to 1899, is given by Hagenmtiller [3]. In the great majority of cases, 

 if not in all, it is very doubtful if these bodies are parasitic organisms 

 at all, so that to refer them definitely to the Sporozoa, and even to the 

 Coccidia, as is commonly done, is in the highest degree premature. It 

 is especially round the alleged parasites of cancer that the dispute has 

 been hottest. The natural eagerness to fathom the causes of the most 

 terrible of human diseases has produced a flood of literature in which the 

 " discovery " of a parasite, and in many cases of a Sporozoan parasite, has 

 been affirmed with complete confidence many times over. But although 

 Korotnef in 1893 gave a complete description of the cancer-parasite in 

 all phases of its life-history, under the name Rhopalocephalus carcino- 

 matosus, the opinion has been steadily growing, and is now held by 

 almost all zoological experts who have looked into the matter, that the 

 bodies which revealed themselves to Korotnef and others as cancer-parasites 

 are nothing more than cell-enclosures of various kinds, either degenera- 

 tions of structures normal to the cell, such as nuclei, " Nebenkerne," etc., or 

 products of abnormal cell-metabolism, supplemented perhaps by leucocytes 

 and other cells in various states of diseased activity and degeneration. 

 Recent expressions of zoological opinion have therefore been sceptical 

 towards the parasitic theory of cancer, relegating the parasites to the 

 realm of fable, or at least pronouncing decisively against their alleged 

 Protozoan nature (see Doflein [2a], pp. 8-11 ; Schaudinn [5 la], pp. 405- 

 408). 



