MENDELIAN RATIO AND CHROMOSOMES 497 
smaller dyad accompanied the accessory. Owing to the decreased 
size of all the chromosomes at this stage, the difference in volume 
of the smaller chromosomes is difficult to distinguish, and to be 
worth anything the figures compared must be not only from the 
same animal, but from the same slide, in order to avoid compli- 
cations due to fixation and staining. Figures 65 to 68 comply 
with these conditions. 
The result is clearly four sorts of spermatozoa. One-half con- 
tain the accessory, and of these again one-half contain one of the 
larger chromatids and one-half one of the smaller. Likewise, 
the spermatozoa without the accessory may be classed as those 
containing the large and those containing the small chromosome. 
5. Spermatids 
Spermatids of Arphia simplex, at the time when the ordinary 
chromatin has become quite diffuse, contain the three condensed 
elements; accessory, large precocious chromosome and one member 
of the unequal pair still in a dense condition. Figures 21 and 22 
are drawings from such a stage of twelve chromosome spermatids, 
with the accessory, of course, present. One contains the large 
and one the small chromosome, c. A comparison of some of the 
features of these two spermatid nuclei with the nucleus at the 
end of the growth period shows the volume to be reduced about 
one-fourth. This, of course, is what might be expected, since 
four cells have been formed from the one with practically no 
resting period between the two divisions. The accessory is 
approximately one-half the volume of the accessory of the first 
spermatocyte which has undergone but one division (figs. 54 and 
55). The large precocious element is beginning to diffuse, hence 
is more than one-half the size of the first spermatocyte dyad from 
which it is derived. The same applies to the derivative of the 
unequal tetrad. 
