142 CARL RICHARD MOORE. 



Ordinary laboratory precautions were observed, such as 

 sterilization of each urchin, hands, and instruments with tap 

 water. 



III. COMBINATION OF PARTHENOGENESIS AND FERTILIZATION. 



A great variety of agents, chemical as well as physical, have 

 been found to be effective in initiating changes within the egg 

 leading to development or partial development. Most of the 

 agents lead to an imitation of the action of the spermatozoon 

 in that cortical changes of the egg are induced by them that 

 result in membrane production. The exception to the general 

 rule seems to be the action of hypertonic sea water and even here 

 accounts vary as to whether or not there is a cortical change in- 

 volved. Membrane production has been recorded following 

 exposure of sea-urchin eggs to saponin, distilled water, lipoid 

 solvents, blood serum, fatty acids and other agents; but more 

 consistent results have been obtained by the use of butyric acid 

 than of any other agent and it is largely this method that has 

 been employed in this study. 



i. The Curve of Fertilization after Butyric Acid Treatment. 



A certain well-known parallelism exists between eggs fei tilized 

 by sperm and eggs that have been subjected to butyric acid 

 treatment. In both cases a membrane is produced around the 

 egg, clearly visible with a low power of the microscope. In 

 both cases this membrane, the vitelline membrane, often called 

 the fertilization membrane, 1 becomes evident almost immediately 

 and very much toughened on standing. The fertilized egg 

 cleaves, gastrulates and later swims: the same is also true of 

 the butyric-acid-treated eggs if they are exposed to hypertonic 

 sea water at the proper time. The end results in the two cases 

 are indistinguishable. Is there then also a physiological parallel- 

 ism between the two kinds of activation? 



It has long been known that an egg once activated by a 

 spermatozoon does not respond to a second sperm insemination. 

 Is this also true of eggs activated by butyric acid? If so when 

 does the egg acquire such a physical or physiological state that 

 it will not respond to the influence of a spermatozoon? 



1 For details of membrane production see Heilbrunn '15. 



