176 T. H. Morgan. 



that this relation is more fundamental, and the particular substance 

 is one peculiar to the whole body. That the reaction must be 

 something quite specific is shown by the fact that the spermatozoa 

 are able to enter eggs of any other individual. 



It appears probable that of all the different substances that 

 excite the spermatozoa to activity the secretions of the glands 

 connected with the male reproductive organs may be the most 

 efficient. From a statement of KoUiker's it seems not improbable 

 that the substance secreted in the glands of one species may be 

 also efficient for the spermatozoa of other species. Whether 

 by the use of the substances from the glands of another mammal 

 it might not be possible to excite human spermatozoa to greater 

 activity and thus assist materially in bringing about fertilization 

 in cases where the impotence is on the side of the male remains 

 to be examined. There is here a question that may have an im- 

 portant practical aspect. 



The lack of power to self-fertilize in plants may also be due 

 to the inability of the pollen tube to penetrate sufficiently far into 

 the stigma and style. It appears that penetration does actually 

 begin in some cases that have been observed, but possibly the 

 growth may be arrested further down in the style. The pre- 

 potency of other pollen would then find its explanation in the 

 more rapid growth of this foreign pollen. Here again is an op- 

 portunity for future work.^ 



In attempting to formulate a theory to account for the deter- 

 mination of sex, Castle assumes that there are two kinds of sperma- 

 tozoa, male and female, and that there are also two kinds of eggs, 

 male and female. He also assumes that a female egg can be 

 fertilized only by a male spermatozoon and that a male egg only 

 by a female spermatozoon. I have already pointed out elsewhere^ 

 that my results do not support this assumption. Castle appealed 

 to the case of Ciona as one in favour of his contention, for the 

 eggs here can not be fertilized by the sperm of the same individual. 

 It is not explicitly stated to the contrary, and the reader might be 

 led to infer from the context that in Ciona all the eggs and all 



1 The experimmts of Myoshi should be especially considered. 



2 Popular Science Monthly. Dec, 1903. 



