FERTILIZATION IN PLATYNEREIS MEGALOPS. 99 



a little farther. Stelnach long ago, later Walker ('99, '11) and 

 Hirowaki have shown that in mammals the prostate secretion is 

 necessary for fertilization. Sea-water, then, might injure the 

 sperm and hinder fertilization by destroying a supporting medium 

 necessary for fertilization. (On this point, cf. Gemmil's ex- 

 periments.) 



Finally, a third explanation is possible: the egg alone is injured 

 through sea-water treatment. The egg, in this case, may be 

 dependent on a substance in the female's body or on some se- 

 cretion of its own necessary for fertilization. Both egg and sperm 

 may need body fluids but sperm may be hardier, egg less resistant.^ 



The seasons of 1912 and 1913 were largely given over to ex- 

 periments to determine which possible explanation is valid for 

 Platynereis. In 1914, many of these experiments were repeated. 

 And I may say at once that the explanation must come under 

 the third head as shown by the following experiments. 



The Experiments. 

 The plan of the experiments is briefly as following: 

 Males and females were cut up separately in dishes of clean 

 sea- water. The bits of tissue were carefully removed, the dish 

 of eggs being handled with utmost care to prevent unnecessary 

 agitation. The eggs and sperm suspensions were filtered after 

 having remained in sea-water for varying lengths of time. 

 Sexual products treated thus are designated "washed eggs" and 

 "washed sperm. "^ 



Males and females were thoroughly dried on filter paper or 

 clean sheer linen. The males were cut up in dried clean watch 

 glasses; the females were cut up in the same way or pricked when 



1 That the resistance of eggs and sperm of both Nereis and Platynereis is unequal 

 would seem probable from the following: If to a Nereis sperm suspension janus 

 green be added the fertilizing power of the sperm is in no wise impaired; or if the 

 dye be added to sea-water the living males absorb it readily without any injurious 

 effect on the sperm. The same quantities of the dye in sea-water is toxic to the 

 egg before or at insemination. Eggs taken from a female Platynereis that has been 

 swimming in a janus green-sea-water solution that is not toxic to the males or their 

 sperm will not fertilize. Cf. also action of nicotine on Strongylocentrotus sperm 

 and eggs as observed by the Hertwigs. 



2 Several methods were used for "washing" sperm and freeing them of sea- 

 water, among others that of centrifuging at high speed for six minutes. These 

 were all abandoned for the method here described. 



