12 SPOKOZOA. 



The H^MOSPORiDiA resemble the Coccidia very closely. 

 Their Ufe- cycle can be described in identical terms and the 

 points of diflference attributed to their becoming adapted to 

 parasitism upon a special kind of cell, viz., the blood- corpuscles : 

 the two orders are thus so closely alhed that Doflein (1901) 

 was led to consider the two as suborders of a single order, the 

 CocciDiOMOEPHA. The H^MOSPORiDiA exhibit an alternation 

 of generations, the asexual process or schizogony alternating 

 with the sexual process leading to sporogony ; but an essential 

 difference from the Coccidia is that there is an alteration 

 of hosts, schizogony taking place in the blood or internal 

 organs of a Vertebrate, and sporogony in the digestive tract 

 or other organs of an Invertebrate. Fertihzation takes place 

 in the stomach of the Invertebrate host, which has sucked up 

 the gametocytes from the blood of the Vertebrate. The 

 zygote, instead of being a motionless body, is a motile vermicule 

 (ookinete), which penetrates the wall of the stomach and forms 

 its oocyst, which increases in size with the growth of the zygote, 

 and only persists while the zygote is producing sporozoites. 

 The absence of spores with resistant cysts is due entirely to 

 the fact that the parasite is always sheltered within the body 

 of one or the other of its two hosts. 



So far as the Amcebosporidia (=:Nbospoeidia) are concerned, 

 their affinities are entirely with the Rhizopoda. The body- 

 form of the sporozoite and the adult is that of an amoeba, 

 and no flagellated stages are known to occur. As remarked 

 by Minchin, " the union of the Telospokidia and Neospokidia 

 in one class — the Sporozoa — ^is a quite artificial arrangement." 

 Practical convenience and common practice alone justify 

 their inclusion in one class. 



The Amcebosporidia comprise the three subclasses Cnido- 

 sporidia, Sarcosporidia, and Haplosporidia. The Cnido- 

 SPORIDIA are a well-defined group and are characterized by the 

 spores possessing the polar capsules. Laveran and Mesnil 

 (1899) described in the spores of Sarcocystis tenella a striated 

 structure representing a polar capsule, and Minchin (1912) 

 was led to include Sarcosporidia among the Cnidosporidia. 

 Later authorities have shown that among the Sarcosporidia 

 there is nothing corresponding to the polar capsule, so the 

 Cnidosporidia, Sarcosporidia, and Haplosporidia are best 

 regarded as distinct subclasses, having no affinities with one 

 another or with the Tblosporidia. 



The Cnidosporidia comprise the orders Myxosporidia, 

 AcTiNOMYXiDiA, and MiCROSPORiDiA, to which a fourth 

 order has been added by Kudo (1931), under the name of 

 Helicosporidia, to include a single species described by 

 KeiHn. Dunkerly (1925), discussing the development and 

 relationship of the Myxosporidia, pointed out that these, 

 like the Volvocace^ among the Flagellates, represent an 



