SPERMATOGENESIS OF EUSCHISTUS FAs ye 
close juxtaposition of the two idiochromosomes. ‘The growth in 
dimensions of this bivalent idiochromosome seems to be due to the 
amount of the vacuolar substance, for the safraninophilous periph- 
ery continues dense and compact. In the following prophases 
this separates again into its two components which have the same 
relative sizes as before their conjugation, indicating that the two 
had not fused. Fig. 68 shows the beginning of this separation 
and fig. 69 is possibly an earlier stage of it; in figs. 71-73 the two 
are completely separated, and from this time on the larger one 
(D) continues as before to lie against the nuclear membrane, but 
the smaller (d) comes to float within the nuclear cavity. A 
little previous to their separation the contained vacuole decreases 
in size (compare fig. 63 with figs. 64-70, 72, 73), and then com- 
pletely disappears (figs. 71, 75, 78). The smaller idiochromo- 
some never shows a vacuole after it has separated from the larger, 
and it appears regularly rounded, while the larger is lengthened. 
‘The smaller one (d) becomes distinctly recognizable among the 
other chromosomes by its smaller volume (figs. 83-86), and 
becomes contricted—probably a longitudinal splitting (fig. 85). 
~The larger one (D) may be distinguished by its dense structure 
- up to the time of fig. 81, but when the autosomes have become 
compact it can no longer be distinguished from them (figs. 83-86). 
Their behavior during the maturation mitoses need be only 
- briefly outlined, and for the sake of completeness, for this was 
fully described by Wilson. Only the smaller idiochromosome 
(d) can be recognized during the first mitosis, and by its charac- 
teristic small size (figs. 88-94, 96). It divides by itself, therefore 
equationally, and is usually placed peripherally in the chromo- 
some plate (figs. 90, 91). The larger one also divides and sepa- 
rately from the smaller, because each second spermatocyte 
receives a total of eight larger chromosomes, namely, six auto- 
somes and two idiochromosomes. Both may be recognized with 
certainty in the second spermatocytes, for there both are uni- 
partite while each autosome is a dyad. Fig. 96, an anaphase of 
the first mitosis, shows only the smaller (d), but both (D,d) in 
figs. 97 and 98 (the latter a polar view of one chromosomal plate). 
In the equator of each second spermatocyte they conjugate again 
