1916] Sicezij: Kinctonndcus of Flagellates 205 



times before the next phase, gametogenesis. The gametes unite to 

 form a zygote which grows to a larger organism and divides again. 

 The Haemosporidia, to meet the exigencies of parasitic life and pro- 

 vide for possible destruction of the host, have evolved another phase 

 of tlie life-cycle which is not found in the free-living forms, namety, 

 sporogony, the production of resistant spores. The life-cycle of the 

 Coecidia shows the same resemblances, differing only in minor details. 



One group only among the Mastigophora offers a life-cycle of this 

 type, the Rhizomastigina. On account of its morphology as well as 

 its life-cycle, which bears a strong resemblance to that of some of the 

 rhizopods, some authors have placed this group as a connecting link 

 between the Rhizopoda and the Mastigophora. The life-cycle of 

 Mastigella vitrea differs from that of the Sporozoa in that schizogony 

 does not occur, and at the same time it cannot be said that it is typical 

 of the process taking place in the Mastigophora. 



The general lack of life-cycle of the sporozoan type in the Mastigo- 

 phora, while it may yet be brought forth by further investigations, 

 does not, at the present time at any rate, suggest a close relationship 

 between them and the Sporozoa. The occurrence of life-cycles of 

 similar types, together with the entire absence of cilia or flagella and 

 the fact that very many genera of the Sporozoa are typically amoeboid 

 in certain phases of the life-cycle, frequently in the trophozoite stage, 

 would suggest closer affinities between the Sporozoa and the Rhizopoda 

 than may be looked for in the flagellate line. Of the two character- 

 istics of the Telosporidia which are said (Minchin, 1912) to ally them 

 to the Mastigophora, the first, the possession of flagellated swarm- 

 spores, must be thrown out entirely as these also occur in the Rhizo- 

 poda; the second, the gregarine-like form of the body, is typical only 

 of the gametocyte generation in some genera, as Plasmodium, and its 

 formation may be compared to the encysted stages which occur in 

 some amoebas at the same period. The whole evidence, as shown in 

 the general outline of the life-cycle and in the morphology, points 

 away from the Mastigophora and toward the Rhizopoda as the group 

 with which the Sporozoa are allied. 



The order " Binucleata, " as it has been thus presented, is com- 

 posed of the haemoflagellates, which possess a structure related to the 

 motor apparatus, the parabasal body, for which nuclear value is postu- 

 lated, and the Haemosporidia, which do not possess a motor apparatus 

 of the flagellate type, but for which the presence of an accessory 

 motor structure is claimed, having the value of the parabasal body 



