H. M. FucHS 237 



impracticable for a further cause. It is impossible to make up sperm- 

 suspensions of identical concentrations each time that sperm is removed 

 from the duct. 



Thus it cannot be decided whether the change in the capacity for 

 self-fertilization shown by the genital products on lying in water is due 

 to a change in the eggs or in the sperm. 



3. Position of genital products in their' ducts. 



The iiTegular variation in the self-fertilization percentages obtained 

 on successive days when an isolated animal is allowed to lay eggs and 

 sperm naturally must be explained in part at least by the differences in 

 the concentration of sperm, depending on the amount ejected on each 

 occasion. The importance of the sperm-concentration has already been 

 shown (pp. 232-233 above), but this may not be the whole reason for 

 the differences in the percentages just referred to. The phenomenon 

 suggests that the genital products of a given animal vary in their 

 capacity for self-fertilization from, day to day. 



This hypothesis can be tested as follows. The eggs lying at the 

 inner end (base), in the middle and at the outer end (top) of the long 

 oviduct are removed separately from the animal and brought into sea- 

 water. The sperm is then removed from the sperm duct and used to 

 fertilize the three lots of eggs separately. 



If equal amounts of the three lots of eggs showed the same amounts 

 of self-fertilization with equal concentrations of the sperm, it would 

 argue a uniformity of behaviour in one animal : although the possibility 

 would not be excluded that the eggs given off from the ovary at a later 

 occasion might act diffei-ently. If, on the other hand, the three lots 

 gave irregular differences in the percentages, it would be clearly shown 

 that eggs produced at one time have a different capacity foi- self- 

 fertilization from those produced at another time, since eggs lying at 

 the top of the oviduct are older than those lying at its base. Thei-e is 

 also a third possibility, namely that a regular gradation in percentages 

 from base to top would be found. 



Experiments were made on this plan, and also the reverse ones of 

 testing samples of eggs, taken from the whole oviduct and well mixed 

 together, with sperm from different positions in the vas deferens. The 

 details of the first series of experiments were as follows : 



The oviduct of an animal was clipped in one or more places and the 

 eggs removed separately from the different lengths thus divided off. 

 Comparative tests were made of the self-fertilizing capacities of these 



