O^i^ 



IV 



SOME METHODS FOR PRELIMINARY 

 EXPERIMENTAL MANIPULATIONS 



The mere handling of living eggs and spermatozoa in the 

 laboratory may influence their viability, their development, their 

 reactions, and thus the results of experiments made with them. 

 The basic rules given above will serve to guard against sources 

 of error due to improper handling. Where, in addition, an 

 experiment demands preliminary manipulations which, them- 

 selves experimental, only precede the experiment to be made, 

 these should be strictly controlled in their effect on the cells; 

 certainly, if they induce abnormalities, these should be of a 

 known and small degree. The truth and importance of this 

 statement are self-evident. 



As yet, very few procedures have been worked out thoroughly 

 enough to serve as reliable methods for such preliminary experi- 

 mental manipulations. In this section, I give as preliminary 

 to experiments a few methods that can be easily controlled in 

 their effect on the cells. These methods are the outcome of 

 scrupulous study through many years; the worker may rely 

 on them. 



Methods for Removing the Jelly 

 FROM the Eggs of Echinids 



For some kinds of experimental work the removal of the 

 jelly enclosing echinid eggs is frequently desirable. This is 

 generally accomplished by treating the eggs with HCl in sea- 

 water. The jelly may also be removed by shaking. Both 

 methods may be injurious to the eggs. 



It has sometimes been stated that the presence of the jelly 

 hulls around echinid ova is necessary for the separation of the 

 vitelline membrane, the normal response to insemination 

 (McClendon, Elder, Gray). Upon this statement theories of 

 the mechanism of memrane-separation have been fabricated. 



41 



