THE H^MOFLAGELLATES AND ALLIED FORMS 289 



a karyosome, and it is surrounded by a space, sometimes purely virtual, 

 which represents the nuclear vacuole, bordered by a delicate nuclear mem- 

 brane, on or close to which the basal granule of the flagellum is lodged. 



In some species of the brucii-group, an axial filament, apparently a sup- 

 porting structure of the nature of an axostyle, has been described (cf. Swel- 

 lengrebel, 514). The system of fibrils, however, with which Prowazek 

 decorates the trypanosome-body are probably artefacts (cf. Minchin, 479). 



Many trypanosomes contain granules in their cytoplasm which stain 

 similarly to cliromatin, so-called " chromatoid grains." According to Swel- 

 lengrebel (514), they are of the nature of volutin (p. 68, supra). 



The division of a trypanosome is initiated, as a rule, by the division of the 

 blepharoplast or basal granule of the flagellum, and following close on this 

 a reduplication of the flagellum takes place, the exact method of which is 

 disputed. In some cases the old flagellum appears to split ; in others the 

 parent-flagellum remains unaltered, and a daughter-flagellum grows out 

 from the daughter-blepharoplast. It is asserted by some that in all cases 

 the new flagellum really arises as an independent outgrowth of a blepharoplast, 

 and that the splitting of the old flagellum is only apparent, and due to the 

 daughter-flagellum growing out at first in its sheath, from which it separates 

 later (cf. Wenyon, 84). The division of the kinetonucleus follows hard 

 on that of the blepharoplast, and next, as a rule, the trophonucleus divides. 

 When the division of flagellum and nuclei is complete the body divides, begin- 

 ning to do so at the flagellar end ; the two sister-trypanosomes are often 

 connected for a time by the posterior extremities. 



The division of the kinetonucleus is a simple constriction into two ; that of 

 the trophonucleus is of a simple type, in which first the centriole and then the 

 karyosome divides. The two daughter-karyosomes travel apart, and the 

 nucleus follows suit. The two daughter-nuclei sometimes remain connected 

 for a time by a long centrodesmose, which is finally severed. Such, at least, 

 is the mode of division of the two nuclei as it has presented itself to the majority 

 of investigators, and the nuclear division of trypanosomes is to be regarded 

 as amitotic, or at least not further advanced towards mitosis than that of 

 Coccidium described above (p. 106, Fig. 51). According to Rosenbusch, 

 however, the division of the nuclei, both trophic and kinetic, takes place by 

 true mitosis. This author is in advance of his contemporaries upon this 

 point, and his statements require independent confirmation before they can 

 be accepted unreservedly, since in objects of such minuteness, requiring 

 delicate and elaborate technique, imagination may all too readily outrun 

 perception. 



Life-History. The transmission of trypanosomes from the blood 

 of one vertebrate host to another is effected, probably for every 

 species of these parasites, by the agency of a blood-sucking inverte- 

 brate of some kind. When the host is a terrestrial vertebrate, the 

 transmitting agent is generally an insect, such as a mosquito or 

 some biting fly or bug, or an ectoparasite of the host, such as a 

 flea, louse, or possibly a tick in some cases ; the trypanosomes of 

 aquatic vertebrates, on the other hand, are transmitted by leeches 

 in all cases that have been investigated. In addition to inoculative 

 transmission (p. 24) of this kind, trypanosomes may pass directly 

 from one vertebrate host to another during coitus ; this is known to 

 occur in the case of the parasite of " dourine " in horses (T. equi- 

 perdum), and has been suspected, but not proved, to take place in 

 other cases also. It is also possible for the vertebrate to become 

 infected by devouring animals containing living trypanosomes, 



19 



