322 THE SPOROZOA 



lowest members of them are taken into consideration. But the 

 forms further from the boundary-line, in each class, are distinct 

 enough, and if a typical member of either group be selected, such 

 as Amoeba for Rhizopoda, and Euglena, or some similar form, for 

 Mastigophora, we are confronted by two sharply contrasted types. 

 It would indeed simplify the comprehension of the two theories of 

 Sporozoan ancestry if they were termed the hypotheses of the 

 amoeboid and the euglenoid ancestry respectively. 



Biitschli in his great work on the Protozoa ([1], p. 807) ad- 

 vanced the theory of the euglenoid ancestry. Given a typical 

 Flagellate which became adapted first to a saprophytic, and then 

 to a parasitic mode of life, it would tend as the result of parasitism 

 to become simplified in characters and to lose all special organs of 

 locomotion, nutrition, and sensation. An Euglena or Astasia, 

 deprived in this way of flagellum, mouth, chromatophores, stigma, 

 and vacuoles, nutritive or contractile, would be practically indis- 

 tinguishable from a simple Gregarine. Considered generally, the 

 body -form, cuticle, and contractile elements of the Gregarines are 

 very similar to those of the typical Flagellata, and the resemblance 

 of the "euglenoid" movements of Gregarines to those of "metabolic" 

 Flagellata has already been pointed out. The same is true also of 

 the motile stages of other Telosporidia; for example, the sporozoites 

 and merozoites of the Coccidia, the ookinete or " vermiculus " of 

 the malarial parasites, and the free haemogregarines of the Haemo- 

 sporea. Since Biitschli wrote, the discovery of flagellated stages 

 in many Telosporidia has given additional support to the Flagellate 

 theory, and has caused Wasielewski to pronounce in favour of it. 



The theory of the euglenoid ancestry of the Sporozoa is, in 

 fact, based chiefly on certain characteristic features peculiar to the 

 Gregarinida and other Telosporidia; but when the attempt is 

 made to extend this hypothesis to the Neosporidia, the case is very 

 different. It must be admitted at once that the Neosporidia have no 

 euglenoid phases, and that the general facies of the group is strongly 

 Rhizopod-like, as pointed out by Doflein [100] and other investi- 

 gators. No Neosporidia are known to have flagella at any period 

 of their life-cycle, and, with the possible exception of the gymno- 

 spores of Sarcosporidia, none of their phases are euglenoid or 

 gregar^niform. On the other hand, many of them are amoeboid, 

 and have the protoplasm naked, without any sort of cuticle or 

 envelope at the surface of the body, throughout the whole trophic 

 period. Typical Myxosporidia can, in fact, be regarded as Rhizo- 

 pods adapted to a parasitic mode of life. In their general features, 

 especially in the formation of the pseudopodia, the structure 

 and relations of the nuclei, and the alternation of generations, they 

 resemble, as Doflein remarks, the Foraminifera most nearly, an 

 indication, perhaps, of a common origin for the two groups. The 



