FERTILIZATION IN PLATYNEREIS MEGALOPS. IO5 



finally become quiescent through lack of oxygen^ in various 

 positions without orientation. After dry inseminations they 

 come to rest, as can be seen after flooding the dishes, definitely 

 oriented and not in haphazard arrangement. Clustered among 

 the jelly hulls, their heads point toward the eggs. On occasions, 

 I believed that I demonstrated the agglutination of the sperm by 

 sea-water in which the eggs had been lying. The evidence is not 

 clear-cut and more recent attempts have failed. The egg 

 charged sea-water, however, does activate the sperm. 



I wish to point out the serious difficulties experienced in the 

 series of sperm agglutination experiments. In the first place, 

 twenty "large" dried males (two and one half centimeters long) 

 do not yield enough sperm and body fluid to make up a drop as 

 large as a drop of dry sperm from a very small Nereis. Then 

 again the thickest suspension got is largely made up of blood cor- 

 puscles. I have never succeeded in procuring a "milky sus- 

 pension" — the admixture of corpuscles and body fluid giving 

 always a pinkish mixture. And finally, one cannot always get 

 twenty or more males necessary to make up even this thin sperm 

 suspension. Repeated efforts, therefore, extending through two 

 seasons have not been marked with very positive results. 



With Nereis sperm, the case is indisputable. If water in which 

 Platynereis have laid eggs be taken it is found to have an agglu- 

 tinating effect on Nereis sperm. Thus: 



August 18, 1914. At 10:15 P.M., ten females laid eggs in six c.c. 

 of sea-water each. After five minutes some of this water was 

 drawn off — 20 c.c. in all. Nereis sperm suspensions were made 

 up fresh at 10:20, 10:30, ii :oo and 11 :05. A drop of the sperm 

 suspension was mounted on a slide under a raised cover slip. A 

 drop of the water taken from the dishes of eggs was injected 

 beneath the cover slip. Under the microscope, the quiescent 

 sperm appeared at first intensely active, then rushed together 

 and formed agglutinated masses among others still free-swimming. 



1 This fact was brought out in 1913 when I was repeating some old observations 

 on echinoderm spermatozoa. While experimenting with the sperm of Thyone in 

 janus green solutions, I noted after some time had elapsed that cover-slip prepara- 

 tions showed that bacteria present previously bluish in color had changed to a 

 decided red. Later observations proved that as the dye was reduced in bits of 

 tissue under the cover slip the sperm quieted down in various positions. 



