428 



SCIENCE 



[N. S. Vol. XXVI. No. 666 



oxygen or the suppression of oxidations in 

 the egg injures the fertilized egg much 

 more quickly than the unfertilized egg. 

 This becomes easily intelligible under the 

 assumption that the spermatozoon causes or 

 accelerates still other processes in the egg 

 than oxidations, e. g., hydrolyses, and that 

 the products of these hydrolyses are util- 

 ized in the processes of oxidation. If the 

 oxidations do not occur the products of the 

 tydrolyses accumulate in the egg or give 

 rise to further reactions not compatible 

 with the life of the egg. It thus becomes 

 comprehensible why the fertilized egg suf- 

 fers miich more readily than the unfer- 

 tilized egg, which seems to be able to stand 

 the influence of lack of oxygen for several 

 days, and possibly a longer period of time. 

 It is of course possible that among the 

 hydrolyses occurring in the fertilized egg 

 might be those of lecithin. 



- Ill 



Our present knowledge of the chemical 

 structure of the spermatozoon does not en- 

 able us to state why the entrance of the 

 spermatozoon into the egg should cause its 

 development. That part of the spermato- 

 zoon which prevails by its mass is its head, 

 which seems to have essentially the same 

 chemical composition as the egg nucleus or 

 any other cell nucleus. The tail of the 

 spermatozoon is cytoplasm which is at pres- 

 ent not characterized by anything special 

 except a relatively large amount of lecithin 

 and f^t. If we wish to gain any further 

 insight into the nature of the process of 

 fertilization we must turn to those experi- 

 ments in which the action of the spermato- 

 zoon on the egg can be imitated more or 

 less completely by well-known chemical 

 agencies. The data on heterogeneous 

 hybridization seem to indicate that the sub- 

 stances which cause the egg to develop 

 3nust be identical or closely related in 



widely different forms, otherwise we could 

 not understand why the sperm of various 

 starfish, of the brittle star, the crinoids, 

 and, according to Kupelwieser, even of 

 moUusks, should be able to fertilize the egg 

 of the sea-urchin. It almost looks as if the 

 only limitation to heterogeneous hybridiza- 

 tion were the fact that for some reason the 

 spermatozoon is not able to enter into the 

 egg of a widely different family. This 

 may explain why it is often necessary to 

 change the constitution of the sea-water, 

 for example, to raise its alkalinity, in order 

 to enable the spermatozoon to enter the 

 foreign egg. It follows from this fact 

 that we can draw conclusions upon the 

 nature of the process of fertilization only 

 from such methods of artificial partheno- 

 genesis as are of a more general applica- 

 tion. 



We shall begin our discussion with a 

 consideration of the methods of artificial 

 parthenogenesis in the sea-iirchin, since 

 they have been most thoroughly investi- 

 gated in this form. The first method by 

 which larvse were produced from the un- 

 fertilized egg of the sea-urchin consisted 

 in treating the eggs with sea-water wtose 

 osmotic pressure had been raised about 50 

 per cent. The method consisted simply in 

 putting the unfertilized eggs for about two 

 hours at a temperature of about 20° C. into 

 a mixture of 50 c.c. sea-water plus 7^ c.c. 

 2^N NaCl and then transferring them to 

 normal sea-water. This method, which 

 gave comparatively constant and good 

 results on Arhacia at Woods Hole, gave 

 unreliable results in a form of sea-urchin 

 common at Pacific Grove, Strongylocen- 

 trotus purpuratus. Neither were the re- 

 sults obtained with this method, on the 

 shore of France and at Naples, very satis- 

 factory, according to reports by Giard, 

 Herbst and others; while E. B. Wilson ob- 

 tained good results with this method on 

 Toxopneiistes at Beaufort, North Carolina. 



