384 



he found a distinct acceleration in the later cleavage stages and subse- 

 quently in the hybrids between Fundulus majalis, female x Fundulus 

 heteroclitus. male. 



GENERAL CONSIDERATIONS AND THEORETICAL. 



SELECTIVE FERTILIZATION. 



In a general consideration of these experiments, perhaps the most 

 striking fact that appears is the uniformity with which it is possible to 

 cross-fertilize the various species of teleosts. The percentage of eggs fer- 

 tilized is in practically all cases a high one — fifty per cent., and, in the 

 majority of cases, seventy-five per cent, or over. When one reflects upon 

 the reason for one's astonishment at this, he finds it in the fact that we 

 have all. those of us who iiave given the matter any thought at all, allowed 

 ourselves to grow into the belief that there is a sort of specific affinity or 

 adaptation existing between an egg and the spermatozoon of the same 

 species. This assumj)tion may or may not be true. So far as the writer 

 has been able to determine, there is extant no evi'dence that this is the 

 case in the animal egg. A possible exception is to be found in the ex- 

 periments of Dungern ("01). who hnds that in the eggs of the star- 

 fish there is a substance which is poisonous toward the sperm of the sea 

 urchin, but not vice versa. It is easy to see that under such conditions 

 the spermatozoa of the starfish would be favored. 



On the other hand, we have experiments by Buller on all the groups 

 of Echinoderms which seem to show that there exists no specific affinity, 

 chemical or otherwise, between the egg and its own spermatozoon. 



The writer is elsewhere publishing a detailed account of his experi- 

 ments on selective fertilization in fishes. It may be proper, however, to 

 briefiy call attention in this connection to a few of the results he obtained. 

 First. The fact above stated, that among these fishes it is possible so 

 uniformly to cross-fertilize the different species lends no support to the 

 "specific adaptation" theory. Second. When a lot of Fundulus heteroclitus 

 eggs are given a chance at a mixturt' of tw(i sperm, one of which is their 

 own and the other a strange species (Menidia. for instance), the eggs do 

 not necessarily show any preference for their own sperm. In the case above 

 mentioned, for instance, the great majority of the eggs pi'efer the Menidia 

 sperm to their own. In other combinations the proportion is about equal. 

 Ip still others the eggs may select more of. their own sperm. The factor 



