6 1 4 TR YP ANOSOMI ASIS 



thus to find the opportunity for passing into the body of a fresh host. 

 Minchin, however, has been unable to find evidence of a sexual stage in 

 this trypanosome. 



A still further development of the views held as to the life-history of 

 the trypanosomes is found in the work of Schaudinn, who investigated 

 the trypanosoma noctuce found in the owl (athene noctua), and which is 

 carried from bird to bird by the common mosquito (culex pipiens). In 

 the blood of the owl is a halteridium hsemamceba showing pigmented 

 male and female forms, closely corresponding to those observed by 

 Macallum in the crow. These, according to Schaudinn, on reaching the 

 mosquito's stomach undergo ordinary changes the microgametocyte 

 develops microgametes, one of which fertilises the macrogamete. An 

 oval motile ookinete results, and in the formation of its nucleus from 

 the male and female elements a reduction of chromosomes takes place, 

 while the superfluous nuclear structures along with the pigment are cast 

 out of the cell. In these ookinetes a differentiation into male, female, 

 and indifferent forms can be recognised, but the important new departure 

 is that each can go on to develop into a trypanosome. In the indifferent 

 ookinete a portion of the new nucleus breaks off by a sort of heteropolar 

 division, and the broken-off part becomes the micronucleus or blepharo- 

 plast of the trypanosome and gives origin to the undulatory membrane. 

 Longitudinal division of these forms in the mosquito's intestine may 

 occur, and here it may be said that Schaudinn differed from other observers 

 in holding that on division the membrane does not split, but that one of 

 the individuals gets its membrane by this being laid down along the root 

 of that already in existence. Further, a resting-stage of the trypanosome 

 may occur, in which it becomes attached to the intestinal epithelium, 

 and, losing more or less its flagellate form, may resemble a gregarine. 

 The female ookinete is plumper and contains more chromatin granules 

 in its protoplasm than the male and indifferent forms, and is in virtue 

 of the reserve material in its protoplasm much more resistant than the 

 male or indifferent forms ; when these die out, as they do when, for 

 instance, the insect is starved, it reproduces all three forms by a process 

 of parthenogenesis. In the female ookinete the smaller nucleus which 

 goes to form the blepharoplast of the indifferent trypanosome divides 

 into eight small nuclei, all of which perish, and the blepharoplast and 

 membrane are formed by a fresh division in the large nucleus remaining. 

 In the male ookinete, which differs from the female in the clearness of 

 its protoplasm, a similar heteropolar mitosis takes place, and again eight 

 small nuclei are produced. These evidently represent the essentially male 

 element, for they persist, and each, appropriating to itself a portion of 

 the cellular protoplasm, detaches itself so that eight small trypanosomes 

 are budded off from the ookinete. This male ookinete Schaudinn holds 

 to be homologous with the microgametocyte occurring in the blood of 

 the owl, and the small trypanosomes are similarly homologous with the 

 microgametes formed when the blood of the host reaches the stomach 

 of the mosquito. These small trypanosomes and the male trypano- 

 somes readily die, probably because, by a reduction process in their 

 genesis, the assimilative powers of the larger nucleus have been 

 diminished. In degenerating they often are found in the intestinal 

 tract of the mosquito arranged in rosettes, with sometimes the anterior 

 ends, sometimes the posterior ends, directed towards the centre of the 

 rosette. The next stage of development takes place when the parasites 

 by the mosquito's bite reach the blood of the vertebrate host, and it is 



