391 



tail, they form no eyes. Occasionally one or two poorly developed ear 

 vesicles show ; pigment is irregularly and rather sparingly developed on 

 both the embryo and the yolk. These cells are practically all black with a 

 few small, poorly developed brownish ones. The heart may develop into a 

 protoplasmic pulsating mass showing no definite form. The pericardial 

 cavity is poorly developed or wanting. These embryos may remain alive 

 for a week or ten days, but never as long as the hybrids of the two pre- 

 ceding groups. 



We can see from the foregoing that within the narrow limits of the 

 species covered, that the more distantly two species are separated in 

 their blood relationship when crossed, the earlier the developmental pro- 

 cesses come to a standstill. The writer, of course, thoroughly appreciates 

 that the foregoing facts are not necessarily evidence in favor of the view 

 taken. He desires merely to emphasize the analogy existing between the 

 conditions of hybridization and the known conditions of blood transfusion 

 and the like. His belief that this analogy is a significant one has been 

 strong enough to lead him into further, more direct experiments along this 

 liiie. The writer may even be permitted to express a hope of his that it 

 may be possible to control the processes of hybridization in a manner sim- 

 ilar to that which has already been brought about in the field of immunity. 



SUMMARY. 



1. The eggs of any of the species of teleosts tried may be impreg- 

 nated by the sperm of any other species tried. 



2. The number of eggs fertilized is usually great, i. e., 75% or more. 

 This bears no relation to the nearness of relationship of the two species 

 concerned. 



3. Normal impregnation is the rule, di- and polyspermy being the 

 exception. 



4. Development in its early stages proceeds normally, the deleterious 

 effects of the two strange sex jiroducts upon each other showing only at 

 later cleavage or subsequently. 



5. The rate of developjnent in the early cleavage stages is always 

 that of the egg species. Any effect of the strange sperm upon the rate of 

 development shows itself by slowing the process regardless of whether the 

 rate of the sperm species is faster or slower than the egg species. 



^ 6. A period of great mortality in the developing hybrids is gastrula- 



