BEHAVIOR OF CHROMATIN IN HYBRIDS 505 



without taking up the cytology of such eggs. Loeb kept these 

 hj'-brids aUve a month or more, and they formed the heart, t)lood- 

 vessels, eyes, and fins, though they never hatched. He beheves 

 that the sperm in these cases acts as a parthenogenetic agent, 

 simply removing from the egg obstacles to its division. The 

 hybrids are therefore 'pure breeds' and the abnormalities which 

 occur are due to the interference with the normal chemical reac- 

 tions caused by the introduction of a foreign sperm. These 

 abnormalities are, he says, "in no sense hybrid characters" and 

 he ciaused similar abnormalities by keeping normally fertilized 

 Fundulus eggs in sealed Erlenmayer flasks containing 50 cc. sea- 

 water -f 2 cc. 0.01 per cent NaCN. In two instances, however, 

 he finds in ^Nlenidia eggs fertilized with Fundulus sperm, red 

 chromatophores such as are common in Fundulus eggs but are 

 not present in normal JVIenidia eggs. This seems like genuine 

 inheritance of a paternal character — the only evidence of such 

 inheritance he has found in these experiments. 



Alany writers in discussing the purely maternal character of 

 heterogeneous hybrids explain this one-sided inheritance by an 

 elimination of the paternal chromatin which may take place in 

 the early cleavages. Among these are Kupelwieser ('09), Baltzer 

 ('10) and Tennent ('08 and '12). Kupelwieser fertilized sea- 

 urchin eggs with mollusk sperm and found that although the 

 eggs divided, the sperm had no part in this division. It lies at 

 the side or at one pole of the spindle and probably degenerates 

 in the 2-cell stage. He did not, at this time, get larvae old enough 

 to show whether the characters were purely maternal or not. 

 Later ('12) he fertilized Echinus eggs with the sperm of an anne- 

 lid, and found that although the pronuclei almost always fuse 

 before the first cleavage, the behavior of the male chromatin in 

 the first cleavage spindle is always abnormal, and it is not in- 

 cluded in the daughter-nuclei of the 2-cell stage. He traces the 

 abnormalities of the larvae, which are maternal in character, to 

 mechanical disturbances of the maternal chromatin caused by 

 the undivided mass of male chromatin on the spindle. 



Baltzer made various crosses between Echinus, Strongylocen- 

 trotus. Sphaerechinus, Arbacia, and Antedon, and found in many 



