636 FERTILIZATION 



and in the others two or three develop into micronuclei and macro- 

 nuclei, while the remaining one or two degenerate. 



In Euplotes patella, the macronucleus and the micronucleus are never 

 sister nuclei, so that the first amphinuclear division evidently separates 

 the macronuclear line from the micronuclear line. However, there is no 

 apparent difference, except one of position, between the two products 

 of the first division. 



In "group C" Kidder lists twelve ciliates, in which differentiation 

 occurs after the third amphinuclear division. To this list, which includes 

 the familiar Varamecium caudatum, may be added Parachaenia myae 

 (Kofoid and Bush, 1936). The number of products, if any, which de- 

 generate appears to vary with the author, as well as with the species. 

 In about half of these species, all nuclei remain functional. 



In Paramecium caudatum, four of the eight amphinuclear products 

 become macronuclei and are distributed by fission to the four grand- 

 daughters, while four become micronuclei. According to Calkins and 

 Cull (1907), all of these micronuclei remain functional and are dis- 

 tributed by fission; but Maupas (1889), Jennings (1920), and Doflein- 

 Reichenow (1928) indicate that three degenerate, while the fourth 

 remains as the functional micronucleus and divides at each subsequent 

 fission, just as it does in P. putrinum (Doflein, 1916). 



In some material, both of these schemes are represented in P. cauda- 

 tum; but, perhaps because the dividing micronucleus is more easily 

 identified, the latter type is more clearly and unquestionably demon- 

 strable. 



In "group D," in which differentiation occurs after the fourth amphi- 

 nuclear division, Kidder lists only P. multimicronucleata (Landis, 1925), 

 Kidderia [Conchophthrrius) mytili (Kidder, 1933a), and Bursaria 

 truncatella, according to Prowazek (1899). But Bursaria belongs in 

 "group C," according to Poljansky (1928, 1934). 



After the final division of the synkaryon, which separates macro- 

 nuclear elements from micronuclear elements, the micronuclei return to 

 the normal condition. This involves shrinkage in size and the restora- 

 tion of the chromatin to the homogeneous condition. If more than the 

 normal number are formed, they are separated by the subsequent body 

 fissions until the normal number is established, as in P. caudatum, 

 according to Calkins and Cull (1907). If the normal number were 



