744 
Digby.—The Somatic , Premeiotic , and 
bear the same significance as the fission present before synapsis. The 
fission could again be recognized in the loops as they escaped from the 
second contraction (PL LXII, Fig. 56). It will finally divide each univalent 
chromosome into the two daughter chromosomes in the homotype division 
(PL LXIII, Fig. 75). The fission is only to be seen for the extremely 
short interval when the newly differentiated univalent chromosomes are 
still flattened and uncondensed (Fig. 59 B). As soon as they are con¬ 
centrated and rounded, the split is once more obscured to reappear in 
Galtonia as the chromosomes approach the poles (PL LXIII, Fig. 68). 
The two individuals which constitute each bivalent chromosome may 
break apart at once, or they may remain for a time joined at one end, so 
as to form a loop (PL LXII, Figs. 60 and 6i). Often, in such loops, one 
limb is seen to be composed of homogeneous chromatin, whilst the other 
limb consists of large chromatin beads (Fig. 61) alternating with linin areas, 
the chromatin not having yet concentrated. This is strikingly like the 
figures of King ( 14 ) in Bufo> except that in Bufo each chromatin portion 
represents a single univalent chromosome, and the intervening faintly stain¬ 
ing areas the points of future transverse cleavage between the chromosomes. 
When the segments have but newly split, it is possible to identify the 
eight pairs of chromosomes (Figs. 57 and 60). Apparently the large pairs 
of chromosomes are joined to form long loops (Figs. 60, 61, and 62). The 
individual chromosomes are attenuated (Fig. 60) as compared to their 
appearance in the later stages (Fig. 62). The two pairs of small chromo¬ 
somes are always in advance of the others. They are the first to be 
isolated from the second contraction (Figs. 55 and 56), the first to split 
apart (PL LXI, Fig. 53), and the first to become concentrated (PL LXII, 
Fig. 60). When differentiated they are often in the form of a single 
sausage-shaped mass, which splits into a pair of somewhat bean-shaped 
chromosomes (Figs. 56, 59 b, and 60). One or other of the small pairs is 
nearly always in contact with the eu-nucleolus (Figs. 62 and 63). Wilson 
( 34 ) (1905, 1) has shown that the larger idiochromosome in Lygaeus 
bivalens and the accessory chromosome in the Hemiptera ( 35 ) (1905, 2) 
are in the same way attached to the plasmosome. Stevens ( 29 ) in Trir- 
habda has found a similar association in the case of the irregularly paired 
heterochromosomes. 
On the differentiation of the eight pairs of chromosomes there is a rapid 
concentration and thickening of the individuals (Figs. 62 and 63). The 
members of each pair always remain close to one another. Strands of linin 
traverse the nucleus. Sometimes one or more of the pairs may be con¬ 
nected to form a chain (Fig. 63) as in Tradescantia ( 22 ) and Oenothera ( 1 ). 
Before diakinesis the chromosomes become much contracted and are very 
thick, and stain densely. The small chromosomes are usually round, the 
larger ones are more rod-like (Fig. 64). Then the nucleolus fragments 
