l62 DYNAMICS OF LIVING MATTER 



{Triton alfestris). When the eggs of the toad (Bufo vulgaris) are fer- 

 tilized with the sperm of Rana fusca, they develop beyond the morula 

 stage.* Born hybridized various kinds of toads.f 



It is rather remarkable that all these experiments seemed to indicate 

 that the fertihzing power of a spermatozoon is quite specific, and that 

 it does not go beyond the closely related forms. It was of considerable 

 interest to find out whether the stimulating power of a spermatozoon 

 might not be extended to more distant species. Nobody had succeeded 

 in fertilizing the eggs of the sea urchin with the sperm of the starfish, 

 and I had myself vainly tried to accomphsh this result until it occurred 

 to me that by altering the constitution of the sea water this result might 

 be accomplished. The sea water has normally a practically neutral 

 reaction. If, however, just enough NaHO or Na^COj is added to 

 make its reaction faintly alkaline, the eggs of the sea urchin, Strongylo- 

 centrotus purpuratus, can be fertilized by the sperm of every starfish 

 which has thus far been tried, and by that of Ophiurians.% It suffices 



for this purpose to add i to 2 c.c. — NaHO to 100 c.c. of sea water. 



The relative number of sea-urchin eggs that can be fertilized in this way 

 by the sperm of starfish or brittle star varies for various forms. With 

 the sperm of Asterias ochracea, Asierias capitaia, and an Ophiurian, as 

 many as 50 per cent of the eggs could be fertilized, while with the sperm 

 of the twenty ray starfish [Pycnopodia spuria) only 5 per cent, and with 

 the sperm of Asterina only i per cent. In normal sea water only ex- 

 ceptionally an egg of Strongylocentrotus is fertilized by the sperm of 

 Asterias; and in this case the fertilization occurs very late, — from 

 twelve to thirty-six hours after the sperm has been added. The sperm 

 of Pycnopodia and Asterina was never able to cause a fertihzation of 

 the sea urchin's egg in normal sea water. 



It seems that the increase in the alkalinity of the sea water increases 

 only the fertilizing power of the spermatozoon, and not that of the egg. 

 When the sperm of starfish is introduced into alkaline sea water in which 

 there are eggs of Strongylocentrotus, it takes from five to eight minutes 

 before the fertihzation membrane — which indicates the entrance of a 

 spermatozoon into the egg — is formed. After a short time, which 

 varies with the concentration of the HO-ions in the sea water, the sperm 

 loses its fertilizing power, and the spermatozoa agglutinate with each 

 other. The eggs, however, do not lose their power of being fertilized 

 by remaining in tliis abnormal solution. If the spermatozoa of the star- 



* Pfluger's Archiv, Vol. 29, p. 48, 1882. 

 t Born, ibid.. Vol. 32, p. 453, 1883. 



j Loeb, University of California Publications, Vol. I, pp. I, 39, 85. Pftuger's Archiv, 

 Vol. 99, pp. 323, 637; Vol. 104, p. 325, 1904. 



