August 28, 1914] 



SCIENCE 



317 



other a corrective agency whicli guarantees a 

 normal development. 



The third group of factors involved in the 

 process of fertilization is that determining the 

 entrance of the spermatozoon into the egg. 

 This note will deal with the latter problem. 



2. We can undertake the analysis of the con- 

 ditions necessary for the entrance of the sper- 

 matozoon into the egg from two different start- 

 ing points, namely, by finding means for fer- 

 tilizing the eggs with the sperm of distant 

 species against which the egg is naturally im- 

 mune; or by rendering the eggs immune 

 against sperm of their own species. The 

 former problem was solved for certain cases 

 when the writer found that the eggs of the 

 sea urchin {Strongylocentrotus purpuraius) 

 which under normal conditions can not be fer- 

 tilized by the sperm of the starfish or holothu- 

 rians can be fertilized with such sperm if the 

 sea-water is rendered more alkaline. 



Last winter the writer found that an addi- 

 tion of calcium chloride to sea-water acts in 

 the same way. In this case the above-men- 

 tioned hybridization can be brought about if 

 little or no alkali is added to the sea-water. 

 This suggested the idea that the forces deter- 

 mining the entrance of the spermatozoon into 

 the egg depended upon the concentration of 

 calcium and hydroxylions in the sea-water. 



3. If this idea was correct it was to be ex- 

 pected that the elimination of these two sub- 

 stances might render the eggs which are nat- 

 urally fertilized in normal sea-water immune 

 against sperm of their own species. This was 

 found to be the case. If eggs and sperm of 

 Arhacia or purpuratus are freed from sea- 

 water and put into a neutral mixture of 

 NaCl :+ KCl or NaCl + MgCl,, or of 

 NaCl -f KCl + MgClj (in the concentration 

 and proportion in which these salts exist in 

 the sea-water) no egg is fertilized. Tet it can 

 be seen that sperm remains motile in these so- 

 lutions for a long time (twenty-four hours or 

 longer) and it can also be shown that newly 

 fertilized eggs are able to segment in these so- 

 lutions. If calcium chloride is added to these 

 solutions fertilization wiU take place at once. 

 The same is true when a trace of a base is 



added to the mixture of NaCl -f MgCL or of 

 NaCl + KCl + MgCL. 



On the other hand, these eggs can be fertil- 

 ized by sperm of their own species in neutral 

 solutions containing calcium, namely NaCl + 

 CaCl, or NaCl + KCl + CaCh, or ]SraCl + 

 CaCl, + MgCl^ or NaCl -f KCl -f MgCl, + 

 CaCh. Similar results were obtained in re- 

 gard to the fertilization of the eggs of an 

 annelid (Chwtopterus) and a mollusk (Cum- 

 ingia). It can, therefore, be stated that the en- 

 trance of a spermatozoon into an egg of its 

 own or foreign species is determined by forces 

 which are infiuenced by the concentration of 

 calcium and hydroxylions in the solution, the 

 difference in both cases being only in the con- 

 centration of these substances required. 



4. The question arises which forces in the 

 egg or spermatozoon are influenced by these 

 two agencies. Since it seems tolerably certain 

 that neither the strong base nor the calcium 

 salts enter into the egg or the spermatozoon, 

 the forces acted upon by these substances must 

 be located at the surface of the egg or sperma- 

 tozoon. There are only three kinds of forces 

 that need be taken into consideration ; namely, 

 (1) surface tension, (2) adhesion between 

 spermatozoon and egg surface, (3) cohesion or 

 degree of fluidity of the surface of the egg. 

 Experiments which the writer carried out last 

 winter in Pacific Grove seem to indicate that 

 the adhesion of the spermatozoon to other bod- 

 ies is strongly influenced by both calcium and 

 bases. The egg of the sea urchin is surrounded 

 by a jelly which the spermatozoon must pene- 

 trate before it reaches the egg. If it should 

 stick to the inner surface of the jelly it might 

 still come in contact with the egg and might 

 be able to impart to the surface of the egg, the 

 membrane-forming substance; but through its 

 adhesion to the jelly it might be prevented 

 from entering the egg. The egg should, in con- 

 sequence, be in the same condition as one in 

 which the membrane formation has been in- 

 duced by butyric acid but which has not been 

 treated with the second corrective factor. It 

 should show a membrane formation and a be- 

 ginning of development, but should then 

 perish. 



