86 Papers from the Department of Marine Biology. 



obtain a very definite idea of the physiological condition of any sample 

 of eggs by ascertaining the extent of certain changes in size, shape, 

 dissolution of jelly layer, retardation of rate of membrane formation, 

 and rate of cleavage and total cleavage, all of which, and possibly 

 others, serve as different and corroborative indices of their physiological 

 condition. The nature of the chemico-physical factors involved in 

 these variations was made known from a study of aging eggs. 



From this it follows that for a study of the physiology of the germ- 

 cells, or for any experimental work that involves a comparison of germ- 

 cells from different individuals, it is not sufficient to use eggs of the 

 same chronologic age, but by actual tests, as shown above, to choose 

 eggs of the same physiologic age i. e., eggs most nearly in the same 

 physiologic condition. If this be done we should expect less conflicting 

 results than have obtained heretofore. 



CONCLUSIONS. 



1. The optimum conditions of temperature, volume of sea-water, sur- 

 face exposure, and concentration of eggs and of sperm were ascertained. 



2. The eggs and sperm used in these experiments were immediately 

 removed from freshly collected sea-urchins. 



3. Three species of sea-urchins were used, Toxopneustes and Hipponoe 

 of shallow tropical waters and Arbacia of deeper, colder waters. The 

 fundamental results for all these were in entire accord. 



4. The Arbacia germ-cells are less variable than either of the tropical 

 forms. 



5. Variability, with respect to cleavage, differs with different individ- 

 uals. The eggs of one female when fertilized by a given male may give 

 markedly different percentages of cleaving eggs when fertilized by a 

 second male. The difference is usually much greater, all other condi- 

 tions remaining constant, when eggs of different females are fertilized 

 by the same male. The relative difference is usually constant. Some 

 females have a high percentage of cleaving eggs ; other females a low 

 percentage. Cleavage is a function of the kind of eggs used. 



6. The variations studied were: size and shape of eggs; presence of 

 jelly envelope; membrane formation; cleavage. 



7. There is a surprising range of variability for each of these charac- 

 ters and characteristics, less for size or shape, greater for jelly and 

 membrane formation, and greatest for cleavage. 



8. The eggs of some females showed little variation in size from the 

 norm, were usually globular, and a large proportion had the character- 

 istic jelly envelope. These eggs were in good physiologic condition. 



9. The eggs of other females varied considerably in size from the 

 norm, had a high percentage of elliptical eggs and a low percentage of 

 intact jelly envelopes. These eggs were in poor physiologic condition. 



