280 BIOLOGICAL LECTURES. 



Though I do not wish to go into the technicalities of these 

 experiments, I must mention a few of the precautions that I took 

 in order to guard against the possible presence of spermatozoa 

 in the sea water. The reader who is interested in this tech- 

 nical side of the experiments will find all the necessary data 

 in my publication in the American Jotirnal of Physiology (8). 

 Here I only wish to mention the following points : 



i. These experiments were made after the spawning season 

 was practically over. 2. Bacteriological precautions were taken 

 against the possibility of contamination of the hands, dishes, 

 or instruments with spermatozoa. 3. The spermatozoa con- 

 tained in the sea water lose, according to the investigation of 

 Gemmill (9), their fertilizing power inside of five hours if dis- 

 tributed in large quantities of sea water. 



4. We have a criterion by which we can tell whether the 

 egg is fertilized or not in the production of a membrane. The 

 fertilized egg forms a membrane and the unfertilized egg has 

 no distinct membrane. None of the unfertilized eggs that 

 developed artificially had a membrane. 



5. With each experiment a number of control experiments 

 were made. Part of the unfertilized eggs were put into the 

 same normal sea water that was used for the eggs that did 

 develop. None of these eggs that remained in normal sea 

 water formed a membrane or showed any development, except 

 that a few of them were divided into two cells after about 

 twenty-four hours. 6. I made another set of control experi- 

 ments by putting a lot of eggs of the same female into a 

 solution which differed less from the normal sea water than the 

 one which caused the formation of blastulae or plutei from the 

 unfertilized eggs. In this case it was shown, that although 

 these eggs received the same sea water as the ones which devel- 

 oped, and although they were injured less than the ones which 

 developed, yet not one single egg formed a membrane or reached 

 the blastula stage. If the sea water had contained any sper- 

 matozoa these eggs should have reached the blastula stage. 1 



1 Through other control experiments I convinced myself that a treatment of 

 eggs or spermatozoa with equal parts of a - 2 g nMgC! 2 solution and sea water 

 diminishes the impregnability of the eggs and annihilates the fertilizing power of 

 spermatozoa in a very short time. 



