144 SEX IN MICROORGANISMS 



flagellate inhabiting the rectum of tadpoles. Fusion of cells was sup- 

 posed to be followed by nuclear fusion, but further development was 

 not reported. The evidence in this case is not convincing and is too 

 incomplete to establish syngamy. 



Order Protonionadina 



In this group one of the most important families is the Trypano- 

 somatidae, which consists of the so-called haemoflagellates. They are 

 uniflagellate and have a characteristic kinetoplast (sometimes errone- 

 ously called a parabasal body) in addition to the nucleus. An 

 enormous amount of research has been conducted on this group, 

 especially the trypanosomes, yet no complete account of syngamy 

 has been produced. 



The early interpretations of sexuality in haemoflagellates by 

 Schaudinn (1904), Prowazek (1904a, 1905), Moore and Breinl 

 (1908), Moore, Breinl, and Hindle (1908), Baldrey (1909), Schil- 

 ling (1910), and Lebedeff (1910), based largely on polymorphism, 

 have mostly been discredited. Doflein (1910) saw the wide variety of 

 morphological types in cultures of Trypanosoma rotatorium but 

 cautioned against calling these "male," "female," and "indifferent" 

 without convincing evidence. In 1926, Wenyon reviewed the descrip- 

 tions of sexuality in Trypanosomatidae as reported in the literature up 

 to that time and concluded that in no case had authors submitted suffi- 

 cient evidence to support the interpretations of sexuality. Since then, 

 additional descriptions of phenomena interpreted as sexual have ap- 

 peared from time to time, especially during the past decade. 



Elkeles (1944) reported possible sexual phenomena for Try- 

 panosojna cruzi as had Chagas (1927) and Muniz (1927) some years 

 earlier. Vanderplank (1944) described two types of individuals for 

 T. congolense and T. rhodesience. In the latter species, one type had 

 two paired and two unpaired chromosomes (72=6), and the other 

 had two paired and one unpaired chromosome {n=^S). In T. congo- 

 lense one type had three pairs of chromosomes and the other had 

 three paired and one unpaired chromosome. It was supposed that 

 meiosis took place, the unpaired chromosomes acting like the sex 

 chromosomes of other animals, and that gametes so formed would 

 fuse with other haploid cells. Later (1947) the same author exhibited 

 demonstrations showings nuclear divisions with three chromosomes 



