262 



THE AMI- IUC AX NATURALIST [Vol. XLIX 



cial membrane formation if they are either treated for a 

 short time with a hypertonic solution or if for a longer 

 period the oxidations are suppressed in them by lack of 

 oxygen or the addition of cyanide. There is therefore no 

 doubt that the eggs of pur pur at us in which the artificial 

 membrane formation has been induced by butyric acid 

 can be fertilized subsequently with sperm. 



4. The treatment of the eggs of Arbacia with butyric 

 acid leads to the formation of a membrane which varies 

 considerably in the eggs of the same female. Some eggs 

 have a thin membrane which is permeable to the sper- 

 matozoon, others have a tough fertilization membrane 

 which is as impervious to the spermatozoon as the regular 

 fertilization membrane. The percentage of the eggs with 

 membranes permeable for sperm varies very much in dif- 

 ferent experiments, according to the material and accord- 

 ing to the external conditions. If this is kept in mind it 

 is easily understood that the number of Arbacia eggs 

 which can be fertilized after they have been treated with 

 butyric acid differs in different experiments. Since the 

 membrane called forth by butyric acid is not always 

 plainly visible, it is a prerequisite that always one set of 

 such eggs should be set aside as controls to ascertain 

 whether or not all the eggs disintegrate rapidly (if no 

 second treatment is given to them). Only if they all dis- 

 integrate rapidly have we any guarantee that in all of 

 them the membrane formation has been effective. The 

 former experiments of the writer show that such eggs 

 can be fertilized by sperm; in fact they show that while 

 the unfertilized eggs disintegrate rapidly after the in- 

 ducement of the membrane formation with butyric acid, 

 the subsequent fertilization of such eggs by sperm saves 

 their lives and makes them develop. 6 

 Ill 



1. It is a well-known fact that most eggs can only be 

 fertilized by sperm of their own or a closely related 

 species. The writer thought that in order to obtain light 



eLoeb, Arch. f. Entwcklngsmech., XXXVIII, 416, 1914. 



