THE SPOROZOA 321 



Kecently, however, the parasitic theory has been revived by Feinberg, 1 

 who asserts that in sections of young growing cancerous tumours, before 

 the cells have begun to degenerate, there are to be found, between the 

 proliferating tissue-cells, structures consisting of a membrane enveloping 

 a protoplasmic body containing a nuclear corpuscle. Feinberg considers 

 that these bodies are intrusive organisms totally distinct from the tissue- 

 cells and their enclosures and products, and from his comparative studies 

 upon the structure of the nuclei in various animal and vegetable tissues 

 or unicellular organisms, he is further of the opinion that these parasites 

 are indubitable Protozoa. The parasitic theory of cancer is therefore by 

 no means dead yet ; but the Sporozoan nature of the alleged parasites is 

 far from being proved. 



THE AFFINITIES AND PHYLOGENY OF THE SPOROZOA. 



In recent times no zoologist has called in question the position 

 universally assigned to the Sporozoa amongst the Protozoa. The 

 attempts that have been made to establish kinship for them outside 

 this sub-kingdom can scarcely be said to belong to modern zoology. 

 The question remains, however, to which of the other classes of 

 Protozoa the Sporozoa are most nearly allied. Assuming, as every 

 evolutionist must, that all parasites are descended from free-living, 

 non -parasitic ancestors, the problem that presents itself is to 

 determine as far as possible the nature and affinities of the 

 ancestral Sporozoa and their relationship to the three remaining 

 classes of Protozoa the Khizopoda, Mastigophora, and Infusoria 

 respectively. It may be said at once, however, that the Infusoria 

 (Ciliata and Suctoria) need not be considered in this connection, 

 since the Sporozoa exhibit no characteristics linking them specially 

 to this very well-defined group. 



Two rival theories of Sporozoan ancestry have been put forward 

 by competent authorities the one claiming for them descent from 

 the Khizopoda, the other from the Mastigophora. In considering 

 these opposing views, it should be borne in mind at the outset 

 that the Khizopoda and Mastigophora are two' classes which are 

 connected by. many links, and may be said almost to merge into 

 one another at certain points: Many Rhizopoda have swarm- 

 spores, or other stages in their life -cycle, which are flagellated ; 

 many Mastigophora, on the other hand, are amoeboid. Such forms 

 as Mastigamoeba can only be distinguished from true Rhizopoda 

 by the retention of a flagellum in the free stages of the life-cycle ; 

 were the flagellum lost, when adult, as in other cases, the organism 

 would be classed as a Rhizopod. The distinction between the two 

 classes is, therefore, somewhat arbitrary and artificial when the 



1 "Zur Lehre des Gewebea und der Ursache der Krebsgeschwiilste," Deutsche med. 

 Wochenschrift, xxviii. (1902), No. 11 ; and other memoirs. 



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