THE AMERICAN NATURALIST [Vol. XLIV 



Godlewski did not find it necessary to resort to artificial means 

 in causing the spermatozoon of Antedon to penetrate the egg of 

 Echinus, but by an intrenious method Loeh s was enabled to cause 

 the egg of a member of one phylum to be fertilized by the sperma- 

 tozoa from a member of a different phylum. Kupelweiser 9 after- 

 wards applied Loeb's method to a cross between the mussel, 

 My til ii* and the echinoderm, Echinus $, the method involving 

 a subjection of the eggs to a hypertonic solution of sea- water, as 

 in artificial parthenogenesis. Bataillon 10 believes that only arti- 

 ficial parthenogenesis is operative in this ease, basing his con- 

 clusions partly upon analogous crosses in amphibians, where he 

 has crossed Triton $ with the toad Pelodytes 5, and observed 

 that no sperm asters formed and segmentation proceeded without 

 any | >art ii-ipation on the part of the sperm nucleus. 11 Of course 

 if Bataillon 's contention is correct, the case is of no interest in 

 the present connection, but if the two cases are not parallel, 

 Loeb has overcome what we may grossly term sterility, by arti- 

 ficial means, by modifying the osmotic pressure and the permea- 

 bility of the egg-membrane so that the spermatozoon of the 

 foreign species may enter. Sterility here then may be due to 

 purely mechanical factors. Yatsu has pointed out that the 

 failure to procure crosses between the frogs Rana sylvatica $ and 

 Rana virescens is due to the fact that the heads of the sperma- 

 tozoa of the latter are too large to enter the eggs of the former. 

 Here, again, a purely mechanical factor is involved. 



While no experiments have been performed to my knowledge 

 to determine whether a kind of acclimatization may be induced 

 in hybrids, yet some experiments performed by botanisis shed 

 some light upon this point. ( ijirtner, 1 - AYichura 1 "' and Niigeli 1 ' 4 

 believed that fertility decreased in later generations, but 

 Naudin, 15 C. C. Hurst 16 and others, including DeVries, 17 believe 



8 Loeb, J., Eoux's Archiv, Bd. 26, Heft 3. 



8 Kupelwieser, H., Eoux's Archiv, Bd. 27, S. 434. 



Kupelwieser)," Eoux's Archiv, Bd. 28, S. ( 43^48^ 1909. 



"Bataillon, E., "Impregnation et I'Vcon.lation, " Comptes Eendus, 11 

 Juin, 1906. 



"Gartner, 1849, " Bastarderzeugung im Pflanzenreich. " 



♦Nageli, C. v., 1866, " Botani.selic Mitthcihmye 

 d. Wiss., 13 Jan., 1866. 



B Naudin, Ch., 1869, "Nouvelles recherches, ' 



