146 SEX IN MICROORGANISMS 



short and intermediate (cf. three types mentioned by Fiennes for T. 

 congolense). All forms were said to have six chromosomes (possibly 

 three pairs of chromatids). In a suspension in Ringer 's-glucose solu- 

 tion, the following events usually took place within 20 minutes: two 

 trypanosomes approached and intertwined, their centers making con- 

 tact but their ends free. After a short time the anterior end of each 

 fused with the posterior end of its mate, producing a fusiform body 

 with two nuclei and a flagellum at each end. After a time, these fusi- 

 form bodies divided at the middle, producing two trypanosomes. 

 Sometimes before the fusiform body divided one partner appeared to 

 degenerate and the other might or might not free itself. Instances were 

 found of more than two flagellates fused together. Similar conditions 

 were observed on stained slides. Sometimes head-to-head fusions 

 also took place. In T. siviiae identical processes were seen. The 

 authors stated that in blood trypanosomes syngamy could be induced 

 by almost any marked and sudden change of environment. Each of 

 the three forms, long, intermediate, or short, could fuse with itself 

 or with either of the other two. That is, sex in T. rhodesieuse was 

 not obviously related to morphology. (This statement is interesting 

 since most other authors have made differences in morphology the 

 basis of sex differentiation.) The authors considered that syngamy 

 was an adaptive process in which two flagellates associated to ex- 

 change three chromosomes. (Such an exchange of a haploid set of 

 chromosomes would correspond to conjugation in the ciliates.) The 

 authors noted that Hoare (1936) had reported somewhat similar 

 phenomena in T. congolense in blood films and interpreted the ap- 

 pearances as autoagglutination or agglomeration. Agglutination is 

 also suggested by the lack of distinctions between uniting forms 

 noted above. Cytological evidence for the "exchange of chromo- 

 somes" was not presented. 



In 1951, Culwick, Fairbairn, and Culwick reported that when 

 they inoculated a mixture of T. rhodesieuse and T. briicei into rats 

 the resulting infections were different from the parent strains. Cycli- 

 cal transmission of this infection by Glossina morsitans did not restore 

 the morphology seen in the parental types. Hybridization was con- 

 sidered an explanation, and similar results were obtained when T. 

 ganibiejise and T. hnicei were the "parent" species. However, the 

 notorious polymorphism of all three of these species might well cast 

 doubt on the interpretation given. 



