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THE AMERICAN NATURALIST [Vol. XLIV 



in one case. With Sphcerechinus and Strongylocentrotus 

 several chromosomes were eliminated in the anaphase of the 

 first segmentation stage, which were excluded from the nucleus 

 of the resulting cells, when the nuclear walls were formed. Cor- 

 relative with this, the plutei showed abnormalities and the gen- 

 eral resemblance was to the maternal species. Apparently here 

 the case is different from that of Moenkhaus 's Fuudulus-Mcnidia 

 hybrids, for the chromatin of the egg in part at least, is not 

 adapted to association with that of the eggs of the other 

 species. If this interpretation is correct, we may refer the ab- 

 normalities of the hybrid produced from the cross of Sphare- 

 cJtinus to the loss, during the segmentation stages, of chromo- 

 somes derived from the female. The analysis cannot be pushed 

 farther back, in this case, for we are unable to understand why 

 these chromosomes which are excluded from the reconstructed 

 nucleus are ''incompatible'' with those of the egg-nudeus. 

 Whatever the cause, it is probably similar to the auu'lutini- 

 zation of erythrocytes, spermatozoa, bacteria and other cells 

 in the fluids from other organisms or in artificial media. In 

 this connection, it is interesting to recall that Guyer and Jordan 

 found the abnormalities in the testes of hybrids appearing first 

 during the synapsis period, when the chromosomes from paternal 

 and maternal sources conjugate two-by-two, either end-to-end 

 or side-by-side (probably side-by-side in ehordates, according to 

 the observations of Winiwarter). Recent study of spermato- 

 genesis and oogenesis points to the conclusion that the maternal 

 and paternal chromosomes remain dislinct and more or less iso- 

 lated from one another in the primary germ cells, from the time 

 of fertilization until synapsis, and then for the first time are 

 they intimately associated into pairs, as Montgomery suggested 

 — a view which has been abundantly confirmed by Sutton, Ste- 

 vens, Wilson, and a number of others. Here, then, would it be 

 expected that incompatibilities, if ever present, would become 

 apparent. If the phenomenon is of the same category as agglu- 

 tinization, hemolysis and the like, it should be possible to render 

 the sex-cells of one animal immune to the lytic action of those 

 of other animals, on the principles of immunization and anti- 

 body development. In a case, however, where such a relation 



of the same kind. I refer to the auto-immunity of Cynthia, 



