390 THE PROTOZOA 



derived without difficulty from that of the haemamoebae ; and, in spite of 

 the hiatus in what is known of the life-cycle, there is no difficulty in comparing 

 and homologizing the phases of Hcemoproteus columbce with those of a malarial 

 parasite, and consequently with those of a coccidian. The development of 

 Leucocytozoon requires investigation, but the little that is known namely, the 

 schizogony. sexual phases, and ookinetc -formation is entirely of the 

 haem amoeba -type. 



More striking than in any other type of the Haemosporidia are the coccidian 

 features of the hsemogregarines. In such a form as H. stepanowi the life- cycle 

 is seen to exhibit not merely a general similarity to that of the Ceccidia, but 

 even a special resemblance to particular forms. The mode of gamete -forma- 

 tion is that which characterizes the family Addeidce among Coccidia, and the 

 many developmental similarities between H. stepanowi and the only known 

 coccidian parasite of a leech, Orchedbius herpdbddlce, have led Reichenow 

 to derive them from a common form. In many haemogregarines, apparently, 

 the parasite obtains an entry into the vertebrate host, not by the inoculative 

 method, but by the contaminative, through the vertebrate devouring the 

 invertebrate host. In such cases (H. muris, H. gerbilli) the characteristic 

 coccidian sporocysts reappear in the sporogony. It is not necessary, however, 

 to dilate further on the coccidian affinities of the haemogregarines, since they 

 are recognized by Hartmann and his school, and the latest revisions of the 

 order Binucleata do not comprise the haemogregarines, which are left in the 

 Telosporidia. 



As regards the piroplasms, It is perhaps unsafe to generalize in the present 

 fragmentary state of our knowledge of tne life-cycle, and in particular of the 

 sexual phases ; but so far as it is known, the phases of the development appear 

 to correspond closely with those of the typical Haemosporidia. But at least 

 it can be said that the development of piroplasms does not afford the sb'ghtest 

 support to the view that they are in any way allied to Haemoflagellates ; 

 indeed, it can be affirmed, on the contrary, that, of all the forms included in 

 the Haemosporidia, the piroplasms exhibit the least indications of* flagellate 

 affinity. 



From a general consideration of the life-cycles of the typical Hsemosporidia, 

 such as the hsemamoebae and hsemogregarines, and omitting doubtful forms, 

 it is very clear that what may be called the nucleus of the group bears a close 

 and unmistakable resemblance to the Coccidia. One section, comprising the 

 haemamoebae, halteridia, and leucocytozoa of birds, are to be derived from an 

 ancestor which formed gametes after the manner of Coccidium, and in these 

 types the phenomena of " exflagellation " can be observed readily. In the 

 other section, comprising at least the hsemogregarines, gamete-formation is 

 of the type of that seen in Addeidce, and does not take place until the gameto- 

 cytes have associated ; consequently exflagellation in vitro does not occur, 

 but coupling of the sporonts, as in gregarines, has often been described, but 

 wrongly interpreted as copulation (cf. Sambon and Seligmann). 



In the face of such profound homologies with Coccidia, what are the argu- 

 ments from the developmental cycle in favour of a contrary opinion ? The 

 case for the alleged Haemoflagellate affinities of the Haemosporidia rests on 

 the famous memoir of Schaudinn (132) on the blood- parasites of the Little Owl, 

 a work which must now be considered briefly. 



The Little Owl (Athene noctua) harbours the full number of known avian 

 blood-parasites namely: (1) a proteosoma ; (2) a halteridium ; (3) a small 

 form of trypanosome ; (4) a large form of trypanosome ; (5) a leucocytozoon : 

 (6) a spirochaete. 



According to Schaudinn, these six forms belong to the life-cycle of three 

 species of parasites. First, the proteosoma (1) is a distinct form, not related 

 to any of the others. Secondly, the halteridium ( 2) and the small trypanosome 

 (3) are alleged to be two phases of the same parasite. Thirdly, the large 

 trypanosome (4), the leucocytozoon (5), and the spirochaete (6), are supposed 

 to represent different phases of one and the same life-cycle. 



The halteridium (H&moproteus noctuce) was stated by Schaudinn to be the 



