208 CHARLES L. PARMENTER 



and Hoy ('16, p. 356) review other cases of fragmentation in 

 Ascaris megalocephala (Boveri, '99, '04), Angiostomum (Schleip, 

 '11) and Fragmatobia (Seiler, '13). 



In Amby stoma tigrinum (p. 179) and in Salamandra maculosa 

 (Delia Valle, '09, fig. 11), and as stated above, in Oenothera, the 

 fragmented portions are directly in line with the main portion 

 of the chromosome. This may be due to the absence of chro- 

 matin on the Unin or failure of the chromatin to stain at that 

 point. The fact that in several cases (e.g., /, figs. 5, 6 and 7) 

 the space between the fragment and the main portion of the 

 chromosome was uniformly faintly stained lends support to the 

 suggestion. Other cases exhibited connections consisting of 

 various amounts of strongly stained chromatin (e.g., chr.f., figs. 

 5, 14, 15, and 21). AH mitoses in the gill plates (the most iii 

 prophases, fig. 5) showed the largest number of instances of this 

 condition; the peritoneum contained scarcely any. This might 

 be explained as an effect of inferior fixation (p. 173) were it not 

 for the fact that a considerable amount of apparent fragmenta- 

 tion is present, even in the metaphases of the tail epithelium 

 which are fixed under the most favorable conditions. The 

 reason for this is not clear. 



F. The existence of pairs 



The question whether the chromosomes exist in a duplicate 

 series is significant in two respects: 1) in its relation to the 

 mechanism 'of heredity as suggested by Janssen's chiasmatype 

 theory and by the brilliant work of Morgan and his co-workers; 

 2) as a further index of the constancy of the organization of 

 the chromatin. This constancy is vitally related to the theory 

 of the individuality of chromosomes. 



It will be convenient to consider separately the evidence of 

 the existence of pairs in the germ cells and in the somatic cells. 



a. Pairs in germ cells. Van Beneden's ('83) hypothesis, that 

 one-half of the chromosomes of an individual are of maternal 

 origin and that the other half are of paternal origin, has been 

 verified in manv cases. That this double set of chromosomes 



