STUDIES IN THE EXPERIMENTAL ANALYSIS OF SEX. 163 
Professor M. F. Guyer published in 1900 an interesting 
paper (2) on spermatogenesis of normal and hybrid pigeons^ 
and lie described the occurrence of beaded spermatozoa in 
the sterile hybrids similar to those which I have found and 
figured, but he does not allude to any definite abnormality of 
size in the spermatozoa except in a few cases. With regard 
to spermatogenesis, Guyer describes the normal process in 
ordinary male pigeons, and also the process in his hybrids, 
and he found various abnormalities in the maturation 
divisions of the latter, especially in the first maturation 
division, these abnormalities consisting in the frequent for- 
mation of multipolar spindles, nnd in irregularities of the 
synaptic process. His conclusion is that there is something 
i-epelliint in the two germ-plasms which go to make the 
hybrid, of such a kind that the synaptic chromosomes which 
ought to fuse together before the reduction division repel 
one another or fuse abnormally, and that this condition 
upsets the normal equilibrium of the cell, so that it divides 
atypically. 
The result of my own observations is to confirm Guyer’s 
idea substantially, and to supplement his account with certain 
positive details which give a complete explanation of the 
occurrence of the giant spermatozoa we have described, and 
also throw a strong light on the cause of the sterility of 
these hybrids. 
The process of maturation in the normal male pigeon and 
dove may be first described, but only the main points need be 
considered here, as my observations agree with those of Guyer 
in every particular (2). Figs. G-8 on PI. 8 show the impor- 
tant stages in the normal pigeon and dove. The primary 
spermatocyte in the first maturation division shows eight 
rounded chromosomes arranged regularly on the mitotic 
spindle, these chromosomes being approximately equal in size. 
There is no evidence of the existence of an odd or acces- 
sory chromosome at this or any other stage of the process. 
'I’he chromosomes which appear on this mitotic spindle 
have often the appearance of rings. There can be no doubt 
