344 GARY N. CALKINS 



(figs. 28 and 29) and the fusion of granules to form the chromo- 

 somes parallels their origin in higher forms. 



c. The second maturation division. In all ciliates in which th© 

 number of chromosomes has been accurately counted, the reduc- 

 tion in number occurs during the second maturation division. 

 This was first made out in the case of Didinium nasutum by 

 Prandtl ('06), who found that the sixteen chromosomes resulting 

 from the first maturation division, were separated into two 

 groups of eight each in the second division. This method of 

 reduction appears to be characteristic for ciliates and agrees with 

 what Goldschmidt ('05) designates the 'first type of reduction' 

 exemplified among metazoa by Zoogonus mirus. 



Prior to Prandtl's work there were no conclusive observations 

 on reduction in ciliates. Maupas ('88) and Hertwig ('89) made 

 no attempt to follow the chromosome history. Prowazek ('99), 

 while mentioning twelve to thirteen chromosomes in the first 

 maturation division of Bursaria truncatella and six in Stylony- 

 chia pustulata, does not give their fate in the second division. 

 Subsequent to Prandtl's work, we find a number' of well-defined 

 cases of chromosome reduction. In Opercularia coarctata En- 

 riques ('07) finds a reduction from sixteen chromosomes to 

 eight, the process agreeing with that in Didinium. In Chilodon 

 uncinatus (Enriques, '08) the same observer describes the four 

 chomosomes resulting from the first maturation division as fusing 

 to form two pairs in the telophase stage. In the second divi- 

 sion each pair divides, the daughter nuclei receiving two chro- 

 mosomes each. A similar fusion of two pairs of chromosomes in 

 vegetative mitosis was observed by Stevens ('10) in Boveria 

 subcylindrica, but she was unable to trace the history of the 

 four chromosomes in the maturation processes. In Carchesium 

 polypinum, Popoff ('08) there are, again, sixteen chromosomes 

 in the products of the first maturation division, which are sep- 

 arated into two groups of eight each by the second division. 

 In Anoplophrya branchiarum, Collin ('09) describes six chromo- 

 somes in the first maturation spindle, each of which is equally 

 divided. The second maturation spindles were not identified, 

 but this excellent and equally candid observer finds only three 



