126 FRANCIS MARSH BALDWIN. 



EXPERIMENTATION. 



In order to procure a sufficient number of eggs for each series 

 of experiments, between one and two dozen large females were 

 opened, and their eggs collected into finger bowls. By successive 

 washing and settling, a uniform mass of mature eggs was obtained, 

 which could be inseminated and divided into two parts ; one to be 

 used for the control, and the other for the experiments. It was 

 found early in the work that the success of the experiments de- 

 pended upon having batches of eggs which were sufficiently 

 mature and uniform, so that all eggs reached successive stages in 

 their development at practically the same time. It was also 

 found that great exactness in the time-relations of the operations 

 was absolutely essential, and that any variation once entered 

 upon was sufficient to make the results worthless from a com- 

 parative standpoint. Usually two series of experiments were 

 started in a day; one in the morning to be carried over to the 

 gastrula stage by the following morning, and one in the afternoon, 

 to be examined the following afternoon. After extended pre- 

 liminary experimentation, it was found convenient, in any one 

 series, to keep the time of exposure constant and to vary the 

 concentration of substance used, although in a considerable 

 number of experiments the opposite procedure was adopted, i.e., 

 the time was varied and the concentration kept constant. 



Practically the same procedure was observed throughout the 

 entire experimentation. At each of the successive intervals 

 after fertilization, usually ten minute intervals, about one half 

 of medicine pipette containing a suspension of the inseminated 

 eggs was placed in a small corked Erlenmeyer flask, containing 

 50 c.c. of the solution of the alcohol in sea-water, and allowed 

 to remain for the time of exposure chosen (usually five minutes). 

 After the given time had nearly elapsed, the excess liquid was 

 poured off, and the eggs with a little of the liquid were placed in 

 a watch glass and the immediate results of the treatment were 

 observed under the low power of the microscope. At the ter- 

 mination of the time of exposure, the watch glass containing the 

 eggs was carefully immersed in a large volume of sea-water in a 

 finger bowl and the water was changed several times to rid it of 

 the excess substance. Finally the eggs were very carefully 



