TRYPANOSOMES OF FISH 603 



of the leech, Piscicola geometra (Fig. 245). Brumpt (1904) observed the 

 development of enormous numbers of trypanosomes in the stomach of 

 Hemiclepsis marginata which had fed on infected fish, and Leger, L. (1904e), 

 made a similar observation with species of Piscicola fed on loaches infected 

 with T. barhatulcB. BrumjJt (1905) succeeded in infecting young carp and 

 two bull-heads by exposing them to the bites of leeches. Brumpt then 

 traced the development of T. granulosum of the eel in H. marginata, and 

 of various trypanosomes of marine fish — T. solce and T. cotti in Trachelob- 

 della punctata, and T. scyllU and T. rajce in Pontobdella muricata. In the 

 case of T. granulosum, he noted that after multiplication had taken place 

 in the stomach of the leech the flagellates migrated forwards and passed 

 through the proboscis into the proboscis sheath, whence infection of the 

 wound inflicted by the proboscis took place. Neumann (1908, 1909) 

 described the development of T. giganteum and T. variabile of the skate in 

 the leech {Pontobdella), and was able to infect Raja punctata with T. varia- 

 bile by means of P. muricata (Fig. 246). 



Cycle in the Leech.— Robertson (1907) has studied the trypanosomes 

 in P. murciata, and suggested the possibility of their being derived from 

 the trypanosome (T. rajce) of the skate (Fig. 247). A further contribution 

 (1909, 1909a) to the subject was made by this observer, and the flagellates 

 of the leech were definitely associated with T. rajce. The first stages of 

 development in the leech, according to Robertson, is a rounding-oft" of the 

 trypanosome, with loss of undulating membrane and flagellum (Fig. 247, 

 i-io). The latter is finally cast ofi from the body, and may continue its 

 movements in this free condition for some time. The rounded cytoplasmic 

 body resulting from this change then undergoes division. The whole 

 process can be watched under the microscope in a fresh blood-preparation. 

 The single nucleus can be seen at the centre of the parasite, and its division 

 into two can be followed. After division of the nucleus the cytoplasm 

 divides, and two smaller bodies are produced. These in their turn divide, 

 and the four daughter individuals repeat the process. In a film thirty-six 

 hours after preparation there were present still unaltered trypanosomes 

 actively motile and non-motile individuals in groups of four, six, or 

 eight. At about this stage in the daughter forms there appear short 

 stiff rods which by gradual growth become flagella. They seem to take 

 about twelve hours or more to become motile. The flagellate forms 

 thus produced are more or less rounded, and by change in shape and 

 elongation, during which further multiplication occurs, various types of 

 flagellate, some of which have the crithidia forms, arise (Fig. 247, ii). In 

 the leech the rounding-ofl process and division into non-flagellate daughter 

 forms and the early formation of the flagella take place in what Robertson 

 calls the first stage of digestion. The production of the large number of 



