240 SEX IN MICROORGANISMS 



Recently these difficulties have been the subject of a special 

 study by Devide and Geitler (1947) and Devide (1951). In the ac- 

 count of Devide (1951) it is stated that the chromosomes of eucil- 

 iates in the earher literature are not and cannot be chromosomes, but 

 chromosome aggregates, the transverse division of which, so far as it 

 occurs, and the inconstancy of shape and number, do not present any 

 problem for modern karyology. The "true" chromosomes are said 

 to be visible chiefly during meioses, when they pair and form tetrads 

 seen in metaphases where dyads separate. The masking observed in 

 somatic, metagamic, and postmeiotic mitoses can also apply sometimes 

 to meioses. 



Devide used aceto-carmine mostly and described micronuclear 

 divisions and meioses for Colpidhim compylum, Euplotes char on, 

 Oxytricha sp., Chilodonella dentata (= C. uncinata), and mitoses for 

 Opal'ma ranarnm and Cepedea dimidiata. His demonstration of typi- 

 cal tetrads in the first meiotic division of Colpidium compyhim and 

 Euplotes char on are impressive, but not so satisfying for Oxytrica, 

 Stylonychia, or Chilodonella, since clearly defined tetrads are not 

 indicated for these other species. Hence, even with Devide's tech- 

 nique, satisfactory details of meiosis were not always forthcoming. 

 The idea of chromosome aggregates is a useful one and would help 

 to explain such a situation as that seen in Nyctotherus, referred to 

 above (Fig. AK). In the prophase of the first meiotic division of 

 Stylonychia, Devide states that chromatic bodies number well over 

 100 and possibly 300 to 400. With such large and indefinite numbers, 

 it would be very difficult to work out meiotic counts, and one won- 

 ders if, after all, in such stages, the chromatic bodies are not chromo- 

 meres instead of chromosomes. 



Another feature of the meiotic period of conjugation deserves 

 to be mentioned. As already noted, Diller showed transfer of macro- 

 nuclear material from one conjugant to another in Taraviechmt 

 trichium (Fig. AD, 3 to 4). In Nyctotherus cordifonnis (Wichter- 

 man, 1937) conjugants eventually became completely fused in the 

 anterior region so that, presumably, cytoplasm and macronuclear 

 fragments are free to transfer from one conjugant to the other (Fig. 

 AK). In those cases where conjugants fuse partially or completely, 

 as in Metopjis sigmoides, the Peritricha (Fig. AG, 7 to 9), the Chono- 

 tricha (Fig. AH, 5 to 8), and the Suctoria (Fig. AI), cytoplasmic 

 and macronuclear material of the two conjugants may become mixed 



