76 



Papers from the Department of Marine Biology. 



from or 1 per cent to 80 per cent. In other experiments when a few 

 drops of highly concentrated suspension were removed to 10 c.c. of sea- 

 water, almost maximal cleavage occurred 15, 30, and 45 minutes after 

 fertilization. ( See 7/14, B, c, D.) 



In Toxopneustes, therefore, optimum results were obtained when the 

 egg concentration was below 8,000 in 10 c.c. of sea-water in a Syracuse 

 dish and when fertilized by 1 drop of standard 0.05 per cent sperm 

 suspension. In actual experimentation about one-tenth of this 

 concentration of eggs was used, and in all experiments the sea- water 

 was doubly filtered and stored in large quantities, to insure greater 

 uniformity and to guard against evaporation. 



HIPPONOE. 



In Hipponoe the results were essentially similar, except that to 

 obtain optimum results much greater concentration of sperm was 

 necessary with a given concentration of eggs. In experiment 6/16 

 1 drop of 3 tunes standard sperm suspension fertilized only 3 per 



TABLE 2. Hipponoe and Arbacia. Variation in cleavage caused by increasing concentration 



of eggs and sperm. 



'Standard sperm suspension. 

 2 1 drop dry sperm in 2 c.c. of sea-water. 

 3 1 drop dry sperm in 4 c.c. of sea-water. 

 4 1 drop dry sperm in 8 c.c. of sea-water. 

 5 1 drop dry sperm in 16 c.c. of sea-water. 

 6 1 drop dry sperm in 32 c.c. of sea-water. 

 7 1 drop dry sperm in 64 c.c. of sea-w.iter. 



Used 3 drops of this culture for fertilization. 

 Used 3 drops of tliis culture for fertilization. 

 Used 3 drops of this culture for fertilization. 

 Used 3 drops of this culture for fertilization. 

 Used 3 drops of this culture for fertilization. 

 Used 3 drops of this culture for fertilization. 



