H. M. Fuoiis 217 



C7'oss-fertiliKation of soiiie <jf the eggs by .spermatozoa accidentally 

 present in the water. Morgan (9) thinks this probable, since he never 

 got such high percentages as Castle. Nevertheless, in two cases Castle 

 obtained 90 7o of eggs self- fertilized after the animals had been isolated 

 for three days, and it is very unlikely that spermatozoa of Ciona can 

 retain their power of fertilizing after having been for such an extended 

 period in sea-water, even if they are, as Morgan suggests, entangiefl in 

 the branchial basket of the animal. 



Apart from experiments to be described below, in which fertilizations 

 were made with spermatozoa that had been in sea-water for varying 

 intervals, and all of which showed a more or less rapid deterioration of 

 the sperm, the following preliminaiy tests showed me that the activity 

 of the spermatozoa does not last for very long after they have left the 

 vas deferens. 



(1) Unfertilized eggs were removed from four animals at 7 p.m. 

 At the same time, sperm was removed from the sperm-ducts of the 

 same individuals and a mixed suspension made up. At 11.20 a.m. 

 on the following morning, some of each of the lots of eggs were 

 fertilized with sperm ju.st removed from another individual, and in 

 all four cases 100 /,^ of the eggs segmented. Other samples of these 

 eggs, however, when inseminated at the same time with the sperm- 

 suspension made on the preceding evening, showed only one irregularly 

 segmenting egg between them. Evidently the life of unfertilized eggs 

 is much longer than that of spermatozoa in sea-water. (2) Eggs were 

 removed fi-om an individual into sea-vyater at 8 p.m. Fertilized on 

 the following evening at 9.50 p.m., with fresh sperm, 100 "j ^ segmented, 

 although irregularly. (3) A comparatively dilute suspension was made 

 of the sperm of one individual at 8 p.m. At 9.50 p.m. on the following- 

 evening, this failed to fertilize a single egg of a sample just removed 

 from another animal. 



It appears, therefore, that the higher self-fertilization percentages 

 obtained by Castle than by Morgan were probably due to other causes 

 than the presence of spermatozoa of other individuals, since the animals 

 had been isolated for some days. 



Preliminary experiments (in which rigid precautions were taken as 

 described in the following section to exclude the presence of " foreign " 

 spermatozoa) soon convinced me that Ciona intestinalis at Naples was 

 far from being completely self-sterile, and that the degree of self-sterility 

 varied greatly. In many cases no eggs segmented after insemina- 

 tion with sperm of the same individual, in others comparatively high 



