H. M. FucHS -I'll 



After the eggs had been taken from the oviduct, the latter was slit 

 open from end to end and washed out with sea-water to remove all 

 remaining eggs. The vas deferens was then punctured, and a quantity 

 of sperm removed. 



(3) Controls of unfertilized eggs. 



The final check on the possible presence of " foreign " spermatozoa 

 is kept by the unfertilized egg controls, which are a sine qua non to all 

 experiments on fertilization. Out of every lot of eggs used in the ex- 

 periments described below, 1000 or more were kept in a separate dish 

 to which no sperm was added. In no case recorded did a single egg 

 segment in the control. 



In describing the experiments, the genital products of each animal 

 used are denoted by a single letter, the capital type (e.g. A) referring to 

 the eggs of a female and the small type (e.g. b) to the spermatozoa of a 

 male. The cross made by fertilizing the eggs A of one individual with 

 the sperm b of another is then written Ajb. In the case of a herma- 

 phrodite like Ciona, A eggs self-fertilized is written Aja, and A eggs 

 cross-fertilized with b sperm from another individual, Ajb. 



The results of the experiments are tabulated, and in the Tables 

 the numbers given always mean percentages of eggs which have been 

 fertilized, unless otherwise stated. 



In order to illustrate the most usual method of carrying out the 

 experiments an example is given here, which has the further advantage 

 that it shows up a possible source of error which might easily lead to 

 incorrect conclusions if not taken into account. If sea-water is passed 

 through a filter-paper, the first water to come through is distinctly acid. 

 Whereas normal sea-water gave yellow with neutral red, this filtrate 

 gave a pink colour. It will be shown later that small traces of acid are 

 very injurious to spermatozoa, so that if such filtered water be used in 

 the experiments the results will be quite untrustworthy. If a stream 

 of sea-water is run through a filter-paper for five minutes, after this 

 time the filtrate no longer shows any difference in acidity from normal 

 sea-water when tested with the indicator. The point of the experiments 

 to be described was to discover whether such filtered water still has 

 any effect on spermatozoa, due to the possible presence of some other 

 substance derived from the filter-paper. 



The first experiment was made as follows. Eggs A were removed 

 fi'om one individual Ciomi and sperm h from another, by the method 

 already described. The eggs were placed in sterilized sea-water and 



15—2 



