12 BASIC METHODS FOR EXPERIMENTS 



minutes by trial inseminations of the eggs that they will develop 

 under laboratory conditions in a fashion that closely parallels, if 

 indeed it is not identical to the development in nature, he can 

 then set up his experiment on the basis of a sure knowledge 

 concerning the normal condition of the cells at the outset. It is 

 apparent that such information is highly valuable: it at once 

 removes the uncertainty that attends experiments on many 

 living cells whose physiological condition is obscure. For some 

 species of eggs I have established such criteria from normal 

 development. 



In echinid eggs 



I have found for eggs of echinids at Woods Hole, Naples and 

 Roscoff, that one can quickly ascertain the degree of their 

 normality by following their behavior at insemination and after 

 very simple experimental treatment. (Just, 1928/?.) 



1. All echinid eggs that I know will, if they are in optimum 

 condition, separate their membranes after insemination with 

 fresh and active sperm-suspension at so uniform a rate that in a 

 dish of a hundred eggs under the microscope one can observe 

 that all eggs separate their membranes at almost the same 

 instant. If the membranes do not separate fully, becoming equi- 

 distant from the eggs at every point of the surfaces, one may be 

 sure that the eggs are not normal. Eccentric membranes, 

 partially separated membranes and such that are slow in separat- 

 ing indicate that eggs or sperm are in poor condition. 



Use fresh sperm! Perfectly normal eggs may give poor 

 membranes upon insemination with sperm in poor condition. 



2. Unfertilized eggs of echinids, most sharply those of 

 Arbacia, exposed to distilled water separate their membranes 

 while in the dilution in 15 seconds if they are in optimum condi- 

 tion. If they fail to separate membranes or separate them more 

 slowly, they should be rejected for experimental work. Here 

 lies the possible explanation of the failure of workers to obtain 

 membrane-separation in echinid eggs exposed to distilled water 

 as first reported by Schiicking. I have made innumerable 

 observations on the effect of extremely dilute sea-water on 

 unfertilized echinid eggs always with the same result: if they do 

 not separate their membranes, they are in poor physiological 



