CAN A SINGLE SPERMATOZOON INITIATE DEVELOP- 

 MENT IN ARBACIA?! 



OTTO GLASER. 



During the summer of 191 3 while making the camera lucida 

 tracings on which I have based my comparisons between the 

 volumes of the unfertilized and fertilized ova of Arbacia,^ it 

 became necessary, in order to prevent rotation on the part of the 

 eggs, and the consequent necessity of readjusting the focus, to 

 employ very attenuated suspensions of sperm. The result of 

 the highest dilutions used in these experiments, however, gave an 

 unforeseen result since the appearance of the fertilization mem- 

 branes was either very much delayed, or failed entirely to take 

 place. This observation suggested the idea of a mass effect of 

 the spermatozoa, and the possibility that this might play a role 

 in normal fertilization. 



At that time I had already made observations which had con- 

 vinced me that the fertilization membrane in this egg is not formed 

 de novo, but is preformed in the unfertilized egg, and simply 

 rendered visible by changes occurring at the time of impregnation,^ 



The mechanism through which the fertilization membrane 

 becomes visible will be dealt with in detail at another time; for 

 the present it is sufhcient to say that the absorption of water 

 plays an important r61e. It occurred to me therefore that the 

 prevention of this absorption and perhaps the prevention of 

 fertilization itself might be possible even Vith the employment of 

 more concentrated suspensions of sperm, if the eggs were first 

 treated with Ca. As a matter of fact, it was either difficult or 

 impossible to fertilize eggs so treated. The spermatozoa were 

 active enough, but failed to enter, and fertilization membranes did 

 not appear The following protocol is typical : In a small watch 



1 From the Marine Biological Laboratory at Woods Hole, and the Zoological 

 Laboratory of the University of Michigan. 



2 "The Change in Volume of Arbacia and Aslerias Eggs at Fertilization," Bio- 

 logical Bulletin, Vol. XXVI, pp. 84-91. 



2 "On Inducing Development in the Sea-Urchin (Arbacia punctulata), together 



with Considerations on the Initiatory Effect of Fertilization," Science, Vol. 



XXXVIII., pp. 446-450. 



149 



