422 BENJAMIN H. GRAVE. 



of sea water both sexes are excited at once to remarkable activity, 

 and while swimming excitedly they expel their sexual products 

 with violent contractions. Galtsoff has recently shown that the 

 female oyster will spawn if living oyster sperm is added to the 

 water. This is opposed to the published statements by Nelson 

 who has thought that the oyster spawns on particularly warm 

 days and that general spawning on oyster beds is induced by 

 temperature. I am under the impression that he is correct in 

 this statement but the implied conclusion that temperature is the 

 only spawning stimulus may be misleading. He shows, however, 

 that spawning occurs on the peaks of rising temperatures which 

 indicates that changes in temperature upward cause males to 

 shed and hence general spawning by all nearby oysters results. 

 Spawning by oysters may take place at any temperature between 

 68 and 85 F. (Churchill and Nelson). 



It was found in the case of Cumingia that there is no perceptible 

 stimulus from the opposite sex. They appear to spawn quite as 

 readily when isolated as when in the same dish. Experience has 

 shown that the best way to obtain clean eggs in convenient 

 form for study is to wash the animals free from debris and 

 isolate them in small stender dishes half filled with sea water, 

 or enough water to cover the animal. Both males and females 

 will shed their gametes when so isolated. The eggs are thus 

 obtained free from sperm and may be artificially fertilized at will. 

 Drew was the first to use this method and he was under the 

 impression that drying accentuates or constitutes the spawning 

 stimulus. Morgan in 1910 noted that Cumingia will spawn 

 when isolated (Jour. Exp. Zool., Vol. 9, p. 595). He thinks, 

 however, that the presence of spermatozoa in the water may 

 incite the females to spawn more promptly than they otherwise 

 would. The stimulus in this case, if authenic, might be either 

 chemical or physical. One is likely to gain the same impression 

 by watching the spawning of Chxtopleura (Chiton) because when 

 males and females are placed together in a dish of sea water, 

 the males always shed their products first, and are followed 

 promptly by the females. So far as could be learned, however, 

 spawning by the females occurred as promptly without sperma- 

 tozoa as with them. 



