208 
CHARLES L. PARMENTER 
and Hoy (’16, p. 356) review other cases of fragmentation in 
Ascaris megalocephala (Boveri, ’99, ’04), Angiostomum (Schleip, 
’ll) and Fragmatobia (Seiler, ’13). 
In Ambystoma tigrinum (p. 179) and in Salamandra maculosa 
(Della 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 linin 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). All mitoses in the gill plates (the most in 
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 many cases. That this double set of chromosomes 
