The Chromosomes of Euschistus variolarius, Euschistus servus etc. 489 
of the views of some of the adherents of tlie more extreme chromosome 
hypotheses, forcing them to modify the theory of the individuaUty and 
continuity of the chromosomes so far as to admit that there must be an 
interchange of chi’omatin between individual chromosomes and that the 
chromosomes which emerge from synapsis are ‘probably' not identical 
with the original conjugants’ (Wilson, ’12, pag. 422). They do not, how- 
ever, extend this Interpretation to the X Y chromosomes : ‘the degree 
of Union may vary in different cases, involving sometimes no fusion, as 
is suggested by the history of the X Y pah-’ (Wilson, ’12, pag. 417). 
This would seeni to be an inevitable conclusion, otherwise any facts that 
could be assumed to be explained on the supposition of an interchange 
of factors between X and Y would be inexplicable for those forms in 
which no Y is present. 
In analyzing the results of our recent experiments we shall accept, 
for the sake of the argument, the above assumption that there is no inter- 
change of material between the XY chromosomes, and also the hypo- 
thesis of male- and female-producing spermatozoa.” 
The maturation divisions of the X Y chromosomes of the sperma- 
tocytes of variolarius and servus were described by Wilson (’06). The 
typical behaviour of these chromosomes is to divide in the first division 
as independent univalents, and to separate in the second division — each 
going to the opposite pole, thus producing a visible morphological dif- 
ference in the resulting spermatids. The X Y chromosomes of variolarius 
are demonstrated in photos 1 to 9. In photo 2 they appear as a tetrad 
at the extreme left of the group — this photo demonstrating that these 
two chromosomes may form as distinct a tetrad as the ordinary chromo- 
somes. In the preparation, the 4 parts are clearly attached though the 
longitudinal and transverse clefts are so deep that they almost obscure 
the connecting chromatin. Compare this tetrad with the cross-shaped 
tetrad in the F 2 group of chromosomes in photo 24. Such a cross-shaped 
bivalent is often met among the ordinary chromosomes of both vario- 
larius and servus. 
The first spermatocyte metaphase groups of chromosomes of vario- 
larius are shown in photos 1 to 4, and they demonstrate that the XY 
chromosomes divide as independent univalents, while the so-called ordi- 
nary chromosomes divide as bivalents. 
In all the photographs every chromosome is present in each group 
and the X Y chromosomes are easily identified. Photos 1 to 4 show 
typical chromosome groups of the first sperniatocytes of variolarius, 
and photos 10 to 12 show typical chromosome groups of the first 
Archiv f. Zellforschung. XII. 32 
