336 GARY N. CALKINS 



view in 1881. Gruber ('87) observed a single micronucleus in the 

 dividing stage of Stichotricha scutellum and followed it through 

 two or three divisions, after which he was unable to detect any 

 trace of micronuclei. He inferred that they become progres- 

 sively reduced in size until they could not be identified among 

 the many macronuclei. He also inferred that the conspicuous 

 micronucleus at the time of division is a product of the fusion of 

 all the minute nuclei distributed throughout the cell, just as the 

 single macronucleus is the fusion product of all the macronuclei. 

 At best this was only an hypothesis. Other cases of fusion have 

 been suspected either during so-called autogamous fertihzation 

 (Ichthyophthirius, Neresheimer, '08; Buschkiel, '11) or during 

 encystment (Stylonychia, Fermor, '12). In no case, except at 

 fertilization, has the fusion of micronuclei been established. 



Nor in Uroleptus mobilis have I any evidence that the reduc- 

 tion of micronuclei at division is due to fusion. The two micro- 

 nuclei at this period are no larger than the five nuclei at an 

 earher stage (figs. 10 and 11). All that I can say is that some 

 micronuclei, after attaining a condition of full mitosis, simply 

 disappear. 



B. Conjugation 



There are approximately 1800 species of ciliated protozoa 

 known to science. In 98 per cent of these the conjugation proc- 

 esses are entirely unknown, while the facts regarding conjuga- 

 tion in the remainder are in many cases only fragmentary and 

 the full history is largely conjectural. In a few instances the 

 story is fairly complete and, verified by different observers, has 

 come to be regarded as the characteristic history of conjugation 

 in all ciliates. How far this is true can only be determined by 

 independent study of conjugation in different species and a study 

 uninfluenced by preconceived notions of what the process should 

 be. The widely diverging accounts of the details in forms like 

 Paramecium (Hertwig, Maupas, Hamburger, Calkins and Cull), 

 Anoplophrya (Collin), Trachelocerca (Lebedew), Ichthyophthirius 

 (Nerescheimer, Buschkiel) show that no uniformity characterizes 

 the phenomena and that, until many more data are obtained, 

 generalizations have little value. 



