H. M. FucHS •241 



attacking tlie problem of the moans by which the immunity of eggs t(j 

 fertilization by " own " sperm is brought about that expei'iments on the 

 influence of egg-secretions on fertilization were begun. This investiga- 

 tion forms Part II of this paper. As the work progressed, so many 

 preliminary questions with regard to the effects of the egg-secretions 

 on normal cross-fertilizations in Ciona and other forms had to be settled, 

 that, at the time of writing, not enough experiments on the influence 

 of the secretions of " own " and " foreign " eggs on self-fertilization had 

 been made to justify publication. 



In Part II it will be shown that the eggs of Ciona secrete a substance 

 into the water which stimulates spermatozoa, both of the same and of 

 other individuals, to effect cross-fertilization. Whether this secretion 

 fails to have the same effect on the self-fertilizing power of spermatozoa 

 of the same individual, or whether some other substance is secreted 

 which actually inhibits self-fertilization has not as yet been settled. 

 But whether such a possibilitj-' is true or not, there seems to be another 

 fiictor intimately connected with the difficulty of self-fertilization, and 

 that is a change brought about in the eggs by the presence of " own " 

 sperm. The experiments which will be described in this section seem 

 to show that if eggs be brought into contact with a sperm-suspension of 

 the same individual, their capability of being subsequently fertilized by 

 " foreign " spermatozoa is diminished as compared with that of eggs not 

 so treated. 



The first series of experiments was carried out as follows. In each 

 instance the eggs of an individual were divided into two lots, which 

 were placed respectively in (1) plain water, (2) an opalescent suspension 

 of "own" sperm. At definite intervals 1 cc. of a "foreign" sperm- 

 suspension was pipetted into each of two dishes containing 22 cc. water. 

 The liquids so prepared were then poured separately on to (1) a drop 

 of eggs from the water, and (2) a drop of eggs fi-om the suspension of 

 "own" sperm. These fertilizations were repeated at intervals given in 

 Table VIII, so that the effects on the eggs of remaining for different 

 lengths of time in "own'' sperm could be compared. 



The percentages of segmenting eggs were counted 80 minutes after 

 each fertilization, and at the same time the percentages of self-fertilized 

 eggs lying in "own" sperm-suspension (2) were counted. Table VIII 

 gives the results of the experiments. 



It should be noted in the first place that the Table shows a decrease 

 in the percentages at each subsequent fertilization, a fact which, as has 

 already been pointed out, is almost certainly due to a gradual decline 



Joiuii. of Geu. IV l(j 



