526 BIOLOGY OF THE PROTOZOA 



cases the second meiotic division appears to be nn accompanied 

 by any of the preHminary activities which characterize the first 

 division. In some the nuclei do not return to a resting condition 

 between the two divisions but in otiier cases, e. g., CkUodon 

 (MacDougall, 1925) the second spindle forms from a resting nucleus. 



In ciliates with a multiple number of micronuclei the number par- 

 ticipating in the second di\ision appears to bear no constant rela- 

 tion to the number derived from the first division. In cases having 

 but one micronucleus in the vegetative stages the numerical rela- 

 tions are fairly constant, two spindles in the second meiotic division 

 being the rule. There are, however, some exceptions. Thus in 

 Parameciuvt hursaria according to Hamlnirger (1S04) one of the 

 nuclei formed by the first flivision degenerates without forming a 

 spindle so that only one nucleus undergoes the second division. 

 Other exceptions are found in Evplotes },ate11a in all VorticellidcB 

 and Ophryoscolecidop examined up to the present time. Here the 

 micronucleus undergoes one or more preliminary mitoses prior to 

 the first meiotic division. In Vorticellidce this unusual diA'ision 

 occurs only in the microgamete while the macrogamete follows the 

 usual history of uninucleate forms. 



In ciliates with two micronuclei both undergo the first maturation 

 division. According to Prowazek (1899) the 4 resulting nuclei of 

 Stylonychia yustulata divide again thus forming S products at the 

 second division. According to Maupas (1S89), however, 2 of the 

 first 4 nuclei of Stylonychia pustidata, and of Onychodroinns grandis 

 as well, degenerate so that only 2 second maturation nuclei are 

 formed. Gregory's (1923) observations indicate that a variable 

 number take part in the second division of O.vytricha j'allax. 



In forms with many micronuclei in the vegetative stage there 

 seems to be no general rnle as to the nimiber which imdergo a 

 second division. Prandtl foinid a \'ariable munber in Didinhnu 

 nasntviir, Prowazek a large number in Bursaria trunrateUa, and 

 Calkins a variable number in Vrolciitvs mohilis, while 1 and 4 

 nuclei are rarely found, 2 or 3 are characteristic. 



In summing up the accumulating evidence on meiotic phenomena 

 in the ciliates the conclusion may be drawn that the histor\' in the 

 main is similar to the history of meiosis in Metazoa. Chromosomes 

 of definite number are characteristic of each species and this number 

 is reduced to one-half during one or the other of the two divisions. 

 There is the same difficulty with these Protozoa that is encountered 

 with Metazoa in regard as to which of the two divisions is the 

 reduction division in the sense of separation of whole chromosomes. 

 The important fact is that the numl)er of chromosomes is halved; 

 it is less important, indeed relatively unimportant, to know which 

 of the two divisions actually brings it about. 



