VARIABILITY OF EGGS AND SPERM OF SEA-URCHINS. 



BY A. J. GOLD FARE. 



INTRODUCTION. 



A clear understanding of the variability in normal fresh eggs and 

 sperm is necessary in order to appreciate and to evaluate the changes 

 that take place in overripe germ-cells. This paper will deal exclusively 

 with the qualitative and quantitative differences of such freshly col- 

 lected sea-urchin eggs and sperm and with the differences in then- early 

 development; it will also furnish a basis for the consideration of the 

 chemical and physical changes in aging or overripe germ-cells in later 

 studies. 



To the directors of the laboratories at Woods Hole and Tortugas I 

 wish to extend my thanks for affording me the opportunity to carry on 

 these researches. 



TECHNIQUE. 



Three different sea-urchins were used, Toxopneustes and Hipponoe 

 at Dry Tortugas and Arbacia at Woods Hole. 



The technique is a modification of Lillie's. As soon as possible 

 after the urchins were collected, the eggs were removed, either by 

 inverting each washed and partly dried individual or by removing the 

 ovaries into separate dishes. The eggs were washed two or three times, 

 allowed to settle by gravity hi graduates, and finally enough fresh sea- 

 water was added to make a given concentration. The dry sperm was 

 collected from each individual separately. From this sperm any 

 required concentration was made immediately before fertilizing the 

 eggs. The tune required to make the different suspensions varied from 

 30 minutes to 2 hours. 



In a typical experiment 5 drops of a standard egg suspension was 

 added to 10 c.c. of filtered sea-water and fertilized with 1 drop (0.05 c.c.) 

 of standard sperm suspension. 



The following characters were studied in some detail: (1) Size of 

 eggs. (2) Shape of eggs. (3) Number of eggs with and without jelly 

 layer. (4) Rate of membrane formation. (5) Number and rate of 

 cleaving eggs. 



The first three are matters of direct observation; the last two require 

 a word of explanation, for I have found that such matters of detail are 



73 



