Apeil 23, 1920] 



SCIENCE 



407 



race and on the left its larger gamete reacts, 

 though but weakly, with the minus race. The 

 smaller gamete is therefore minus and the 

 larger plus. On the assumption that the 

 smaller gamete is male and the larger female, 

 the minus race must be considered male and 

 the plus race female. 



In our previous diagram (Figure 4) we rec- 

 ognize on the left the heterogamic species 

 (Ahsidia spinosa) just discussed, by the out- 

 iprowths back of the larger gamete. That 

 heterogamy has actually been derived from 

 isogamy in this species is rendered probable 

 by Lendner's report (12) of finding a race of 

 the same si)ecies with equal gametes. The 

 broken lines, connecting the unequal gametes 

 on the left with the plus and minus diecious 

 species above, represent the reactions which 

 have taken place and indicate that the larger 

 gamete is plus and the smaller gamete, minus. 

 The isogamic hermaphroditic species below 

 also reacts with the diecious form above and 

 hence its gametes also may be labelled plus 

 and minus. The plus gamete of the lower iso- 

 gamic species may be considered, in the 

 process of evolution, to have given rise to the 

 larger gamete of the left-hand figure as indi- 

 cated by the solid line. This is an orthodox 

 interpretation and consistent with the facts 

 so far discovered for this species. There are 

 some facts, however, which indicate that such 

 is not the necessary course of evolutionary 

 development in all forms. 



It has been shown that although the plus 

 race is perhaps usually more vigorous than 

 the minus, this condition is sometimes re- 

 versed. Some hermaphrodites have predomi- 

 natingly plus and some predominatingly 

 min\is tendencies. Is there any intrinsic 

 reason why, of two equal gametes, the plus 

 should invariably become the larger in the 

 process of size differentiation? I do not be- 

 lieve that there is. If not, we should expect 

 to find forms like the one figured on the right 

 where the plus gamete is represented as 

 having given rise to the smaller of the hetero- 

 gamic pair. In Zygorhynchus heterogamus, 

 we have perhaps such an example. The evi- 

 dence is not entirely conclusive since we have 



obtained reactions as yet only with one of the 

 paired test races and the larger suspensor 

 fails to show outgrowths which might help in 

 distinguishing the imequal gametes when re- 

 acting with other forms. However, the ap- 

 pearance of the reactions between the right- 

 hand figure and the minus race resembles that 

 between the left-hand figure and the plus race. 

 The figure on the left has a minus tendency, 

 the same as its smaller gamete while the 

 figure on the right has a plus tendency also 

 the same apparently as its smaller gameta 

 No one realizes more strongly than the 

 speaker that the specific case under discussion, 

 is in need of more thorough investigation^ 

 Whether or not my suggested interpretations 

 of the right-hand figure proves to be the cor- 

 rect one, it will serve to call attention to the 

 fact that those who define male and female 

 in terms of size differentiation in the sex cells 

 are making the gratuitous assumption that 

 quantitative differences in the gametes are 

 the fundamental peculiarities of the two 

 sexes. I have used from preference, there^ 

 fore, the terms plus and minus because I have 

 wished to speak in terms of the physiological 

 differentiation into sexually dimorphic races 

 established in diecious species rather than in 

 terms of male and female which are defined 

 by differentiation in size of gametes and 

 which conceivably may be secondary eex 

 characters. 



I trust it will be granted that there is some- 

 thing fundamental, common to all the plus 

 races that causes them to react sexually with 

 minus races in the same or in different species 

 and that this same fimdamental something is 

 present also in hermaphroditic forms whether 

 possessed of equal or of unequal gametes. 

 Dr. Gortner and I some years ago started an 

 investigation based upon the assumption that 

 the fundamental differences between the sexes 

 might possibly be bound up with differences 

 in sex proteins. The work was unfortimately 

 interrupted before a definite conclusion could 

 be reached with the delicate blood reactions 

 employed. If we are able to imagine some 

 fundamental biochemical constitution such as 

 a sex protein, common to all the plus proto- 



