FERTILIZATION ON PARTHENOGENESIS. 145 



three second exposure, with the exception that usually all of the 

 transparent jelly layer around the egg was completely dissolved: 

 no membranes were produced and the eggs appeared entirely 

 normal. After six seconds' exposure, however, usually a small 

 per cent, of the eggs showed a distinct membrane, ordinarily quite 

 small, while others had begun to show only very slight indications 

 of a membrane. Membrane production increased in intensity 

 and in number with increase in length of exposure until prac- 

 tically all eggs had produced membranes indistinguishable from 

 membranes produced at fertilization. In this experiment 95 

 per cent, of the eggs had produced membranes following an acid 

 exposure of 20 seconds. 1 Longer acid exposure gave a gradually 

 declining curve of membrane production usually falling off so 

 rapidly that eggs exposed to the same strength butyric acid 

 for i minute produced very small membranes or none at all 

 until finally almost no indication of any cortical change was 

 evident. There is decidedly a quantitative aspect to mem- 

 brane production shown in these experiments, and it is to what 

 shall be called the optimum condition of membrane production 

 that we will direct our attention a little later in this paper. 



As above mentioned the fertilization capacity (indicated by 

 cleavage and development) falls off gradually as the percentage 

 of membrane production increases. When the optimum condi- 

 tions for membrane production are given, fertilization is restricted 

 to a very few eggs or is entirely absent. In very few experi- 

 ments does one obtain 100 per cent, of membranes by butyric 

 acid treatment and usually the percentage of cleaving eggs 

 following insemination, corresponds very closely to the number 

 that did not produce membranes. After an acid exposure of 

 the given concentration, lasting only three to five seconds, 

 insemination causes practically all eggs to produce characteristic 

 membranes; cleavage is essentially normal and a very high 

 percentage of swimming larvee are obtained. With longer 

 exposures (10, 15, 20 sec.) the number of eggs that cleave after 

 insemination is less than with the shorter exposure. This 

 decrease in number of cleavages continues as the length of 

 exposure increases up to one minute or longer when there is a 



1 The optimum time varies slightly under different sets of conditions. 



