264 Studies in the Physiology of Fertilization 



Giona blood was removed from the body in the following way. An 

 animal was washed in a stream of fresh-water. After this an incision 

 was made in the body-wall in the region of the heart, which then bulged 

 out through the cut. The animal was held over a small glass dish with 

 the cut downwards, and the projecting heart was then punctured, so 

 that the contained fluid flowed out into the dish. The comparatively 

 small volume of blood obtainable from one animal was usually in- 

 sufficient for carrying out an experiment, and in such cases the volume 

 of liquid was increased by the addition of sea-water. The possible 

 presence of spermatozoa in the blood was checked in the same way as 

 with the ovary-extract. Unfertilized eggs from another individual were 

 placed in a small quantity of the blood and later on examined to make 

 sure that none had segmented. 



III. Effects of Egg- and Ovary-Extracts on Fertilization 



Percentages. 



1. Cross-fertilization^ of Ciona in egg-extract. 



The first experiments were made to try whether, when cross-fertili- 

 zation of Giona was brought about in the presence of crushed eggs of the 

 same species, the percentage of eggs fertilized was raised or lowered. 

 As in all subsequent experiments the method was strictly comparative. 

 In each experiment, approximately equal numbers of eggs of one 

 individual were placed in equal quantities of (1) sea- water, and (2) 

 extract of the eggs of another individual. After a certain interval equal 

 quantities of well-mixed dilute sperm-suspension from a third individual 

 were added simultaneously to the two lots of eggs and mixed. When 

 in the 4-cell stage, the percentages of eggs fertilized in each lot were 



counted ^ 



TABLE I. 



(The bracketed numbers give the time in minutes after fertilization at which the 

 first 4-eell division was completed.) 



In each experiment the eggs lay in (1) water, (2) extract for forty minutes before fertili- 

 zation. 



Water Egg-extr&ct 



37 (87) 100 (87) 



12 (89) 95 (89) 



3 ly 



is here used to mean the fertilization of the eggs 

 of a hermaphrodite animal by the spermatozoa of another individual. No self-fertili- 

 zations were made in this investigation. 



2 As in all the experiments described in this paper, samples of the lots of eggs were 

 kept unfertilized as controls, to guard against accidental contamination with foreign 

 sperm. This is to be taken as granted in the descriptions of subsequent experiments. 



