The President's Address. By ,/. Arthur Thomson. 149 

 C. — Is the Sex Predestined at a very early stage by the 



CONSTITUTION OF THE OVUM, OR OF THE SPERMATOZOON, 

 OR OF BOTH, THERE BEING FEMALE-PRODUCING AND MALE- 

 PRODUCING GERM-CELLS, PREDETERMINED FROM THE BE- 

 GINNING, AND ARISING INDEPENDENTLY OF ENVIRONMENTAL 

 INFLUENCE ? 



On a third view, the bias towards one sex is established at a 

 very early date — in the germ-cells themselves. 



(a) Two kinds of Ova. 



17. It may be that there are two kinds of ova — some pre- 

 disposed to developing into males, others predisposed to developing 

 into females — a view not inconsistent with the assumption that all 

 ova carry the material basis that can produce a complete equip- 

 ment of both masculine and feminine characters. What evidence 

 is there of two kinds of ova ? 



There is no doubt that some animals normally produce two 

 sizes of ova. In certain cases, e.g. Phylloxera among Insects, and 

 Hydatina senta among Eotifers, there are large eggs which develop 

 into females, and small ones which develop into males. Both 

 develop parthenogenetically, so that the problem is not compli- 

 cated by the influence of the sperm. 



In Dinophilus apatris, according to Von Mai sen, and in a mite, 

 Pcdiculopsis, according to Eeuter, where fertilization occurs as 

 usual, there are large and small ova, respectively female-producers 

 and male-producers. 



One must not too hastily conclude that the size determines the 

 sex, since it may equally well be that the predisposition to a 

 particular sex determines the size. The ovum of relatively greater 

 anabolic bias will gather into itself more reserve material. 

 Perhaps the occurrence of two kinds of ova will turn out to be 

 commoner than is supposed. Thus Baltzer has recently described 

 it in sea-urchins. 



18. In some of the higher Pteridophytes there are two kinds of 

 spores, micro- and macro-spores, which produce respectively male 

 and female prothallia. Professor E. B. Wilson notes that a similar 

 predestination, not marked by visible differences, has been proved 

 by Blakeslee in both zygotes and spores of various species of fungi, 

 and that it has also been demonstrated in liverworts and mosses. 

 He refers in particular to the recent studies of the Marchals on 

 dioecious mosses. " Isolation cultures prove that the asexual 

 spores, though similar in appearance, are individually predestined 

 as male-producing and female-producing ; and all efforts to alter 

 this predestination by changes in the conditions of nutrition, such 



