222 MARY T. HARMAN. 



made the reciprocal crosses. She found that some cytoplasm 

 seemed to be more favorable to foreign sperm than others. In 

 some instances a few chromosomes were eliminated, but those 

 that did remain could be identified as to their paternal or maternal 

 origin. Similar results were obtained by Federley ('13) and 

 Harrison and Doncaster ('14) in hybrids of certain moths. 



In the above cases cited there is no indication that these 

 hybrids may occur in nature, and these offspring were obtained 

 from animals which are accepted as distinct species. In the 

 case of Paratettix, P. BB and P. CC are not yet admitted to be 

 species by taxonomists, and they are known to cross in nature, 

 judging from hybrids obtained in the wild and segregated in the 

 laboratory. The chromosomes of each form are so very similar 

 to those of the other forms in so many ways that it is only with 

 close study that the differences are recognized. Yet, when once 

 recognized it is found to be constant. The chromosomes of the 

 hybrids of Paratettix are different from those of the fish mentioned 

 above in that the parental chromosomes are more alike and that 

 the cytoplasm of the egg seems to be perfectly compatible with 

 the chromatin of the foreign sperm. They are different from 

 those of the moths in that there are the same number of chromo- 

 somes in both forms and there is a complete synapsis with the 

 homologous pairs of chromosomes. 



CONCLUSIONS. 



1. The third pair of spermatogonial chromosomes of BB are 

 bent at the proximal end so as to form distinct hooks. 



2. The third pair of spermatogonial chromosomes of CC are 

 pointed at the proximal end, but there is no bend. 



3. The third pair of spermatogonial chromosomes of the hybrid, 

 BC, is composed of one hooked member and one pointed member. 



4. During the growth period there is no indication of a parallel 

 condition of the chromatin either in the chromatin thread or in the 

 chromosomes. 



5. At the end of the growth period there is evidently the 

 diploid number of chromosomes formed which correspond in 

 relative sizes to the respective spermatogonial chromosomes. 



6. Synapsis does not take place in the thread but at the end 



