300 Studies in (lie Phyxiolvf/n of Fertilization 



XL Summary of Experimental Results. 



1. It" a certain number of eggs of an individual A nf Cioun, in 

 a given aniount of plain sea-water, are fertilized l)y the addition of 

 a certain quantity of a sperm-suspension h of another individual, fewer 

 eggs segment than when approximately the same number oi A eggs in 

 the same amount of sea-water, but this time containing egg-extract, are 

 fertilized by an equal amount of sperm-suspension h. 



2. The rate of segmentation of the eggs is the same in jilain water 

 and in egg-extract. 



3. The extract has an immediate effect in raising the fertilization 

 percentage. 



4. The phenomenon described in (I) is the same in the case of 

 Ascidia. 



5. Ovary-extract of Ciona has the same effect as egg-extract. 



6. In Ciona the fertilization percentage is raised by exactly the 

 same amount by equal concentrations of extract derived from the same 

 animal as the eggs used in the cross, from the same animal as the sperm, 

 and from a third animal. 



7. The extract acts as a aperiir " stimulant " in Ciona and does not 

 affect the eggs. Its presence in a sperm-suspension of a certain concen- 

 tration causes more spermatozoa to fertilize eggs than is otherwise the 

 case, i.e., it increases the " fertilizing power " of the sperm. 



8. The sperm of Strong ijlocentrotus is affected by the egg-extract of 

 the same .species in exactly the same way as is that of Ciona. 



9. In Stvongylocentrotus the stimulating action of the extract con- 

 tinues as long as the sperm-suspension is capable of effecting fertili- 

 zation. 



10. The eggs (if Ciomt, Arbacia. and Strdiigi/locentrotus secrete a 

 substance or substances into the water which increase the fertilizing 

 power of the sperm of the same species, in the same way that the egg- 

 extracts have been shown to do. 



11. The effect of the blood of Ciona on the fertilizing power of the 

 sperm depends on the time that the animals from which the blood 

 is taken have been in the Aquarium. The blood of freshly caught 

 animals increases the fertilizing power of the sperm, while that of 



