218 Shidies in the Physioloijij of Fertilization 



percentages of fertilized eggs were obtained. Potts (13, p. 481) has 

 already observed that the Ciona at Naples is not completely self-sterile. 

 He obtained "nearly 100°/^ of embryos" from self-fertilized eggs — an 

 occurrence which was comparatively rare in my experiments, but 

 which would be accounted for if Potts used very concentrated sperm 

 suspensions. Evidently the race of Ciona at Woods Hole behaves 

 differently in respect to its capacity for self-fertilization from that at 

 Naples'. 



The first preliminary experiments were made on the lines adopted 

 by Castle. Animals were isolated for a number of days in bowls of 

 filtered water and the proportion of self-fertilized eggs in each lot 

 was counted. Although this was a fairly extensive series lasting over 

 a month, subsequent experience showed that it was valueless except 

 in demonstrating that self-fertilization can occur. The different lots 

 of eggs deposited by a given animal on successive days showed very 

 varying amounts of self-fertilization, a circumstance which undoubtedly 

 depended largely on the different amounts of sperm ejected with the 

 eggs. Further, the varying self-fertilization percentages suggested, but 

 by no means proved, that the eggs of one individual vary from day to 

 day in their capability of being self-fertilized. Subsequent experiments 

 proved this surmise to be true. (See pp. 236 et seq.) 



The fact that Ciona at Naples is far from being quite self-sterile 

 and that the extent of the self-sterility varies in different individuals 

 and in the same individual with successive lots of eggs and sperm 

 produced, appeared at first sight to render the investigation of the 

 inheritance of the self-sterility difhcult or impossible. Nevertheless 

 self-fertilization proved always to be very much more difficult to bring 

 about than cross-fertilization. In general a comparatively dilute sperm 

 suspension, but one which was concentrated enough to fertilize 100 % 

 of eggs of another individual, would only rarely fertilize even one to 

 two per cent, of the eggs derived from the same animal as itself To 

 bring about self-fertilization much more concentrated sperm suspensions 

 were necessary, and even then it by no means always followed. Taking 

 this fact into consideration, it is plain that after the limits and con- 

 ditions of the occurrence of self-fertilization have been determined, the 

 problem of the inheritance of the comparative self-sterility is still a 

 feasible one for investigation. 



' Whether tlie form of Ciona iiitestiimlis at Woods Hole is really a distinct variety 

 (var. teiielln) or not seems to be uncertain, especially as the distinsuishiug characters of 

 var. feni-lla are not very definite (8, 12). 



