387 



yond the "blastopore" stage though intergradatious 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 ('00) 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 talces place in those 

 hybrids that are arrested much earlier in their dcA'^elopment. 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 nearly 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, \ arying 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, etc., 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 a 

 pathological embryo, such as one sees when they are subjected to an un- 

 favorable condition, such as foul water, insuflBcient 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 



