no PROBLEMS OF FERTILIZATION 



there are certainly three, and we shall examine the 

 evidence as we proceed. 



Methods of studying egg secretions: The present 

 account concerns marine animals exclusively; sea-water 

 is thus the medium of the experiments. Eggs are 

 allowed to stand in small quantities of sea-water, and 

 in a short time the sea-water is found to contain the 

 substances concerned. For the sake of brevity we shall 

 call this sea-water, egg water. The indicator is a sperm 

 suspension of definite concentration in sea-water, which 

 can be best expressed in percentages of the dry sperm 

 to the sea- water of the suspension; a i per cent sus- 

 pension, i.e., i part of dry sperm to 99 parts sea-water, 

 is a good concentration. The most generally useful 

 method of testing the reactions is to place some drops 

 of the sperm suspension on a slide and cover it with a 

 long cover slip supported by glass rods about i mm. 

 in diameter; the egg water to be tested is then injected 

 into the suspension with a capillary pipette operated 

 by a long rubber tube held in the mouth. By this 

 method one can observe under the microscope all the 

 types of reaction. But some kinds of observations are 

 better made in test tubes or other containers. 



Egg extracts, as contrasted with egg secretions, are 

 prepared by mechanically breaking down the eggs in 

 sea-water, by grinding dried eggs in sea-water, or by 

 plasmolyzing in distilled water. In the latter case the dis- 

 tilled water extracts may be brought to the composition 

 of normal sea- water by addition of its volume of sea-water 

 evaporated to half its original volume. We shall distin- 

 guish such preparations as egg extracts from the egg water 

 containing merely the normal secretions of the eggs. 



