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3 
yond the “blastopore” stage though intergradations to those in which the 
embryos hatch normally and grow into adults, probably fertile creatures, 
and this series is correlated with the systematic relationship existing be- 
tween the two species crossed. 
The work of Guyer (700) on the spermatogenesis of hybrid pigeons 
suggests that in the final formation of the sex products, difficulties arise 
in the synopsis of the male and female chromatim material, resulting in 
abnormal spermatozoa. Stated in more general terms in the final forma- 
tion of the sex cell the developmental and hereditary substances from the 
two parents, fail to work harmoniously, giving rise to abnormal develop- 
ment. It is conceivable that an analogous process takes place in those 
hybrids that are arrested much earlier in their development. Indeed, the 
prevailing habit of thinking of developmental and hereditary determinants 
in terms of units of some sort, suggests at once to our minds some such 
picture as above indicated. In two hearly related species the develop- 
mental mechanisms are so nearly alike that no serious conflicts, so to 
speak, arise except possibly in the very last stages, namely, the forma- 
tion of the sex cells. AS a result, the development may be completed or all 
but completed. When, however, two distinctly related species are combined 
we have to do with two developmental mechanisms that are more divergent, 
and the conflict develops early in the life of the organism with the con- 
sequent modification of development, varying with the relationship. It is 
difficult to find any appearances in my hybrids that specifically support 
this view. It would seem that at least occasionally there would appear 
specific modifications to the influence of the sperm over the egg species. 
Thus it should be expected that the mode and rate of cleavage, the time 
and method of gastrulation, ete., should vary in a manner to be in a 
measure at least due to the specific characteristics of the developmental 
mechanisms of the sperm species. But this is just what one does not 
find. The whole process of hybrid development presents the picture of 2 
pathological embryo, such as one sees when they are subjected to an un- 
favorable condition, such as foul water, insufficient oxygen, unnatural 
chemical media and the like. It is simply an arrest with subsequent 
gradual deterioration of the tissues. Thus the monocular condition is likely 
to result if the optic vesicles fail to form properly and the anterior brain- 
vesicle becoming pigmented in the cyclopian eye, or only one side develops 
the vesicle and becomes pigmented. The slender strangulated heart may 
