CHAPTER XIII 

 THE H^IMOFLAGELLATES AND ALLIED FORMS 



General Characters and Principal Types. Under the term "Hsemo- 

 flagellates " are grouped together a number of forms of which the 

 characteristic, though by no means invariable, habit is alternating 

 parasitism in the blood of a vertebrate and in the digestive tract 

 of a blood-sucking invertebrate host. The group must be regarded, 

 however, as one founded on practical convenience rather than oil 

 natural affinity as a method of classification comparable to that 

 of the gardener rather than of the botanist. The existence of a 

 parasitic habit common to a number of different forms is in itself 

 no proof of genetic affinity or community of descent, and it is highly 

 probable that more than one line of ancestry has contributed, 

 through divergent adaptation, to the composition of the group 

 Hsemo flagellates. The name itself has, moreover, lost much of its 

 significance, since closely allied to the forms parasitic in blood, and 

 inseparable from them in a natural scheme of classification, are 

 other forms parasitic only in invertebrates, or even free-living. 



The chief morphological characteristic of the Haemo flagellates is 

 the possession of two nuclei, a trophonucleus and a kinetonucleus, 

 and the relation of the locomotor to the nuclear apparatus is of the 

 third type distinguished in the preceding chapter (p. 263) ; on this 

 account they are ranked by Hartmann and Jollos (390) as a distinct 

 order of the Flagellata termed the Binucleata. 



The Hsemo flagellates as a group comprise a number of forms 

 which represent in some cases distinct generic types, in others 

 merely developmental phases alternating with other forms in the 

 life-cycles of particular species. The following six generic names 

 represent the more important of these types : 



1. Trypanosoma (Fig. 126, etc.), with a single flagellum which 

 arises near the kinetonucleus, at the extremity of the body which is 

 posterior in progression, and runs forward as the marginal flagellum 

 of an undulating membrane. At the anterior end of the body the 

 flagellum is usually continued as a free flagellum, but in some cases 

 it ends with the undulating membrane. A vast number of species 

 parasitic in the blood of vertebrates and in the digestive tract of 



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