342 GARY N. CALKINS 



chromatin mass of Anoplophrya branchiarum, the granules of 

 chromatin collecting in the center of the first maturation spindle. 

 In Didinium, Chilodon and Anoplophrya, these granules fuse 

 until a definite number of chromosomes result, sixteen in Didin- 

 ium, four in Chilodon and six in Anoplophrya. In Uroleptus 

 there may be such a fusion of granules to form eight chromosomes 

 (fig. 40), or the nucleus may divide without such fusion, the 

 granules being distributed in two equal groups in the daughter 

 nuclei (figs. 38 and 39) . It is tempting to assume that the former 

 mode is typical and that eight chromosomes represent the norn al 

 condition of the first maturation spindle. This assumption 

 would bring Uroleptus in line with the maturation phenomena 

 of higher animals. But the fact of the matter is that I find just 

 as many spindles of one type as of the other, and both types 

 are, apparently, equally potent. 



In no ciliate, in which the number of chromosomes can be 

 counted, does this first division result in a reduction to one-half. 

 Furthermore, there is much uncertainty as to whether the divi- 

 sion of the chromosomes is longitudinal or transverse. Prandtl 

 ('06) could not determine which it is in Didinium nasutum; 

 Collin ('09) was equally uncertain; indeed, he seems to have had 

 some doubts as to whether these granular elements on the first 

 maturation spindle were even to be regarded as chromosomes. 

 Enriques ('08), while admitting the difficulties of interpretation, 

 is convinced that the chromosomes of Chilodon uncinatus are 

 transversely divided. Popoff ('08) did not observe the fact, but 

 assumes, apparently from analogy with conditions in many meta- 

 zoa, that this first division in Carchesium polypinum is equational. 



In Paramecium the chromosomes are not granules, but rods 

 which are too numerous to count. With this form it should not 

 be difficult to determine whether the division of each rod is trans- 

 verse or longitudinal. Owing to the early views in regard to the 

 origin of the first spindle from the crescent, it was generally 

 assumed that division was transverse. Calkins and Cull ('07), 

 however, found that the rods are double when formed and that 

 the pairs are each separated in this first maturation division. 

 Such a longitudinal division would correspond, therefore, with a 



