158 Transactions of the Society. 



dominant production of female polyps, and that groups wholly male 

 could be produced by relative starving. It seems from these experi- 

 ments that in Hydra at any rate the nutrition of the body determines 

 the production of ovary or testis. This corroborates the physio- 

 logical view of sex. It would be interesting, though obviously 

 difficult, to go a step further and inquire whether the fertilized ova 

 of highly nourished females showed any tendency, in normal en- 

 vironment, to develop into female rather than mule or hermaphro- 

 dite polyps. 



38. The case of Hydra suggests a reference to analogous facts 

 in regard to plants. Klebs lias showm that the mode of reproduc- 

 tion in Vaucheria repens is very plastic under environmental in- 

 fluence. By altering the temperature and illumination, for instance, 

 he was able to suppress the oogonia. Prantl found that spores of 

 the Royal Fern and of Cevatoptcris thalictroides sown in soil without 

 nitrogenous supplies developed into male prothallia, that female 

 organs were formed when ammonium nitrate was supplied, and that 

 wholly male prothallia might become wholly female prothallia. 

 Similar results have been obtained for horsetails by Buchtien. 



It is plain, of course, that in cases like fern-prothallia and 

 Hydra, what actually occurred was the inhibition or suppression 

 of one set of sexual organs in favour of another in normally herm- 

 aphrodite forms. Therefore such cases, though suggestive and analo- 

 gous, are not quite to the point. 



39. Against the possibility of environmental influence are Stras- 

 burger's numerous experiments on dioecious Phanerogams, such as 

 Mercurialis perennis, spinach and hemp. He found that changes in 

 illumination, soil, crowding, and so on, had no effect in altering the 

 proportions of male and female offspring. He is of opinion that in 

 such cases the sex is fixed by the time the seed is formed. 



Conclusion. 



40. The general trend of research is certainly towards the con- 

 clusion that in most cases the sex of the future offspring is pre- 

 destined at a very early stage in the germ-cells, though the actual 

 determination may not come about until fertilization occurs or 

 does not occur. The belief which used to be widespread that en- 

 vironmental c mditions sometimes determine the sex of the offspring 

 during development has in greater part yielded to a criticism of the 

 evidence, and to the demonstration given by the cytologists that 

 predestination of the gametes sometimes occurs early in their history. 

 It remains possible that the nutrition of the parents may influence 

 the proportions in which the two kinds of gametes are produced 

 and survive. 



41. I find myself unable to get away from the view that there 

 may be no sex-determinant at all in the usual sense, but that what 



