THE ILEMOFLAGELLATES AND ALLIED FORMS 309 



mental stage of Hcemoproteu-s. Although, however, it is quite 

 possible that some trypanosomes may have a heteromastigote 

 ancestry, all the developmental facts hitherto discovered indicate 

 a cercomonad ancestry with a single anterior flagellum, and there 

 is no concrete evidence of a heteromastigote origin for any species 

 that has been studied up to the present. Trypanoplasms, so far 

 as they have been studied, preserve their biflagellate, heteromastigote 

 type of structure throughout their development in all active phases, 

 and never pass through a trypaniform or crithidial phase. Try- 

 panosomes, on the other hand, show constantly a crithidial phase 

 in the invertebrate host, but have not been observed in any case 

 to be heteromastigote or even biflagellate, except temporarily during 

 division, in any phase of the life-history. Consequently, attempts 

 to subdivide trypanosomes on a morphological or phylogenetic 

 basis must be regarded at present as premature (compare also 

 Laveran, 461). 



II. THE GENUS TRYPANOPLASMA. 



The peculiar distribution and occurrence of the species of this 

 genus has been pointed out above. Originally founded for forms 

 parasitic in the blood of fishes, it now comprises a somewhat 

 heterogeneous collection of species, some of which were formerly 

 referred to other genera of Flagellates. Of recent years, the 

 number of species known to be parasitic in invertebrate hosts has 

 increased, and is increasing rapidly. Such are T. (" Trypano- 

 phis ") grobbeni, found in the gastro vascular system of Siphonophora 

 (Kej^sselitz, 453) ; T. (" Bodo ") helicis, from the receptaculumseininis 

 of Helix pomatia and other snails (Friedrich) ; T. dendrocodi, from 

 the digestive tract of Dendroccelum lacteum (Fantham and Porter, 

 P.Z.S., 1910, p. 670) ; T. vaginalis, from the female genital organs 

 of leeches (Hesse, C.E.A.S., cli., p. 504) ; and T. (jryllotalpce, from 

 the end-gut of Gryllotalpa vulgaris (Hamburger). These examples 

 show that the genus, as at present defined, is of widespread occur- 

 rence. It may be doubted, however, if the various species described 

 should all be placed together. 



The species of Trypano plasma parasitic in blood are only known 

 as yet from, fresh-water fishes ;* they have an alternation of hosts, 

 being transmitted by leeches. The life-history of the intestinal 

 trypanoplasms has not been investigated, but in all probability they 

 have but a single host, which acquires the infection by swallowing 

 accidentally their cysts or other resting stages passed out from a 



* The " Trypanoplasma " stated by Bruce and his colleagues (412, pp. 495, 496) 

 to occur in the blood of birds and in the digestive tract of tsetse-flies was in reality 

 a Leucocytozoon. 



