168 
GEOFFREY SMITH. 
thing more than simple segregation is required to obtain the 
complicated results at present vaguely included under the 
term “ Mendeliaii inheritance,” and it may be suggested that 
tlie cytological evidence obtained from the study of these 
liybrids indicates the kind of physiological basis which may 
underlie some of these peculiar Mendelian results. 
Summary. 
(1) The study is based on the cytological investigation 
of the spermatozoa and of spermatogenesis in normal male 
pigeons and doves, and in three male hybrids produced by 
the mating of a male pigeon with a female domestic dove. 
(2) The ripe spermatozoa of the hybrids, which were 
present in large quantities, besides showing in certain cases 
structural abnormalities, were on the average twice as large 
as the normal spermatozoa of either parental type. 
(3) The first maturation or reduction division in the hybrids 
is abnormal, in that the chromosomes do not enter into the 
normal synapse to produce eight synaptic or bivalent chromo- 
somes, but they are scattered as irregular chromatic masses 
of unequal size on the mitotic spindle, and are irregularly 
distributed to the opposite poles of the spindle. 
(4) The second maturation division in the hybrids is almost 
entirely snppres.sed, the secondary spermatocytes proceeding 
without further division to form spermatids and spermatozoa 
of twice the normal size. Many of these spermatozoa are 
structually normal, apart from their double size, while. others 
are abnormally twisted or beaded. All the spermatozoa were 
probably impotent, since these hybrids and all others of a 
similar kind are invariably sterile. 
(5) 'I'he explanation of the sterility of such hybrids is 
found, in accordance with Guyer’s idea, to reside in the dis- 
turbance of the synaptic division during maturation, this 
disturbance being due to the incapability of the chromosomes 
derived from the specifically different [)arents to fuse to form 
the normal synapses. 
