THE SPOROZOA 323 



adaptive modifications induced by the parasitism are shown chiefly, 

 as in other parasites, in the increased fertility and elaboration of 

 the reproductive phases, the differentiation of the spores, and so 

 forth, points in which some forms are more advanced than others, 

 but in which all are highly specialised, as compared with free- 

 living Ehizopods. 



Thus if the Telosporidia seem at first sight to afford some 

 support to the theory of descent from Flagellate ancestors, the 

 Neosporidia certainly do not, but exhibit most pronounced Rhizo- 

 pod affinities. There is, considered from this point of view, a 

 marked difference between the two subdivisions of the Sporozoa, 

 and those who are greatly impressed by the euglenoid features of 

 Gregarines and their allies might be tempted to postulate an 

 independent origin for each sub-class, and to derive the Telosporidia 

 from Flagellate, the Neosporidia from Rhizopod ancestors. But 

 even in the Telosporidia the evidence afforded by the amoeboid 

 character of the endoglobular Haemosporidia points very clearly 

 to Rhizopod ancestry, and the euglenoid phases of this sub-class 

 can be explained as derived from the primitive amoeboid type of 

 body in just the same way as the higher " metabolic " forms of 

 Flagellata, such as Euglena or Astasia, are related to primitive 

 amoeboid types, such as Mastigamoeba. 



The conclusion is, therefore, that in the present state of our 

 knowledge it is simplest to regard all Sporozoa as descendants of 

 Rhizopod-like ancestors, modified by the parasitism to which they 

 are adapted. One immediate result of the changed conditions of 

 life is that they can dispense with all special organs for ingesting 

 or digesting food, since their nutriment is absorbed at the surface 

 of the body. Hence many Sporozoa have acquired a permeable 

 cuticle, and in consequence a fixed body -form. Such Flagellate 

 characteristics as Sporozoa possess, for example the flagellated 

 gametes of many Telosporidia, are found also among true Rhizo- 

 poda. To complete the argument in favour of Rhizopod ancestry, 

 attention may be drawn finally to the remarkable parasitic 

 amoebae described by Schewiakoff (supra, p. 318), which, if they 

 are really allied to the Sporozoa, seem to prove quite conclusively 

 the Rhizopod affinities of the group. 



