THE H^EMOSPORIDIA 395 



parasitism, and consequent temporary loss of the locomotor 

 apparatus. It may well be, therefore, that some forms now 

 generally included amongst the Haemosporidia (e.g., possibly the 

 drepanidia) may prove, when better known, to be stages of Haemo- 

 flagellates, and to have in reality nothing to do with the true 

 Haemosporidia. 



Affinities of the Telosporidia. From the foregoing discussion, the 

 conclusion has been drawn that the Coccidia and the typical 

 Hsemosporidia are closely allied, sufficiently so to be grouped 

 together in a single order, for which the name " Coccidiomorpha " 

 may be used. In a former chapter (p. 354) the relationship of the 

 Gregarines and Coccidia was discussed, and it was pointed out 

 that there was no difficulty in assuming a common ancestral origin 

 for the two groups a conclusion which, indeed, has never been 

 called in question. The Telosporidia, taken as a whole, may be 

 regarded, therefore, as a homogeneous and natural group, in which 

 the close affinity existing between its constituent members may be 

 regarded as indicating a common phylogenetic origin. If this 

 conclusion be accepted, it remains to discuss the affinities of the 

 Telosporidia as a whole to other groups of Protozoa. It is not 

 unreasonable to suppose that a parasitic group of this kind has been 

 evolved from free-living non-parasitic ancestors, and the question 

 to be discussed is to which of the groups of Protozoa the ancestral 

 form of the Telosporidia belonged. Of the three great classes of 

 the Protozoa, the Infusoria may almost certainly be excluded 

 from consideration in regard to this question, since, in view of the 

 very specialized and definite features of this group, there are no 

 grounds whatever for connecting them with the Telosporidia. 

 There remain, therefore, only the Sarcodina and Mastigophora to 

 be considered. 



At different times two opposed theories have been put forward 

 with regard to the affinities and ancestry of the Sporozoa. One 

 view sees in them the descendants of typical forms of Sarcodina, 

 such as Amoeba (Awerinzew, 890) ; the other derives them from 

 flagellate ancestors such as are represented at the present day by 

 Euglena or Astasia. It is no longer possible, however, to regard the 

 Sporozoa as a whole as a homogeneous group, and the two so-called 

 " subclasses," Telosporidia and Neosporidia, must be considered 

 separately, each on its own merits. The Nerfsporidia are considered 

 at the end of the next chapter. The question here is of the Telo- 

 sporidia alone. For this group opinion is practically unanimous at 

 the present day in favour of a flagellate ancestry, a theory which 

 must be considered critically. 



One of the main arguments generally put forward for the theory 

 of the flagellate origin of the Telosporidia is the existence of flagel- 



