264 THE SPOROZOA 



expressed by Schaudinn, namely, that many Haemosporidia, 

 especially those of cold-blooded Vertebrata, are not disseminated 

 by an intermediate host, but that the infection is a casual one, 

 as in any other kind of Sporozoa. It is evident that the acqui- 

 sition of an intermediate host is an adaptation which is vastly 

 beneficial from the point of view of the parasite, as is shown by 

 the rapidity with which the diseases caused by them spread in 

 countries where the two necessary conditions occur the presence, 

 that is to say, both of the parasite and of its blood-sucking inter- 

 mediate host. The latter in all cases hitherto investigated has 

 turned out to be an Arthropod, within which the sporogony of 

 the parasite takes place, and upon which the oocysts are actively 

 parasitic. A general survey of the life -cycles of Haemosporidia 

 and Coccidia would lead one, however, to believe that primitively 

 the sporulating stages would not have been parasitic upon the 

 intermediate host, but that the latter would have acted merely as 

 a carrier and not as a host, in the strict sense of the word. A 

 life-cycle of this kind remains as yet hypothetical, but may be 

 postulated as a stage in the evolution of the adaptive relation 

 between parasite and blood-sucker, even if non-existent at the 

 present day. 



(c) Classification. The nomenclature and taxonomy of the Haemo- 

 sporidia is in a very confused state. It is not uncommon to find the same 

 form appearing in the literature under three or more different names, 

 or to see the same name applied to designate totally distinct objects. Of 

 recent years, however, much has been done to introduce order into this 

 chaos, and students of the group are slowly but surely coming to an 

 agreement as to the correct names of the different forms of Haemosporidia, 

 in accordance with settled zoological usage. There is still, however, con- 

 siderable diversity of opinion as to the manner in which the parasites 

 should be grouped together. 



Labbe [4] classifies the Haemosporidia, as here understood, under two 

 orders, the Haemosporidia sensu stricto, and the Gymnosporidia ( = Acysto- 

 sporidia of Wasielewski). The first of these divisions comprises the species 

 parasitic for the most part upon cold-blooded animals, in which schizo- 

 gony and sporogony occur in the same host. The Gymnosporidia, on the 

 other hand, are the forms parasitic upon warm-blooded hosts, and owe 

 their name to the fact that no resistent cysts are formed by them in the 

 Vertebrate host, since the sporogony takes place, so far as has been 

 observed, in an intermediate Invertebrate host. Eecent authorities have 

 for the most part abandoned this classification, but in so far as it 

 separates the more primitive forms, without special intermediate hosts, 

 from those in which an alternation of habitat has been evolved, it is 

 probably a useful and, to a large extent, a natural mode of grouping 

 these parasites. Labbe's two orders have therefore been revived by 

 Neveu-Lemaire [88] as two sub-orders of the order Haemosporidia, and 

 they are retained here in this sense, but with the terminations altered, in 



