Jantjaet 8, 1909] 



SCIENCE 



55 



exhibits in a more or less rudimentary form 

 characters that are fully developed and 

 functional only in the opposite sex. In ex- 

 ceptional cases these structures may be- 

 come fully developed or even functional, 

 as we see in the occasional appearance of 

 functional mammary glands in the male 

 mammal, or of fully formed stamens in a 

 female flower; while true hermaphrodites 

 occasionally appear, even in diecious 

 species. This suggests that "male" and 

 "female" are but relative terms that de- 

 note tendencies more or less pronounced 

 but not absolutely separate or distinct. 

 The male or female has accordingly often 

 been regarded as a potential hermaphrodite 

 in which one sexual tendency dominates 

 more or less completely over the other; 

 though, as will be seen, there is reason to 

 regard the distinction between hermaph- 

 rodite and diecious organisms as more 

 fundamental than this. The sexual in- 

 dividiial is thus in some respects compar- 

 able to a Mendelian hybrid; and a number 

 of eminent students of the subject have 

 endeavored to show that it actually is such 

 a hybrid. 



The past decade has witnessed a remark- 

 able change of front in regard to the 

 general problem. Even in very early 

 times it was suspected that sex might be 

 controlled by internal factors; and such 

 has long been known to be probable in case 

 of the honey-bee, where, if the Dzierzon 

 theory be correct, the fertilized eggs pro- 

 duce only females, the unfertilized eggs, 

 males. Until recently, nevertheless, opin- 

 ion has been largely dominated by the view 

 that sex-production is in general controlled 

 by extrinsic conditions. A large number 

 of the earlier researches, and some of the 

 later ones, have in fact seemed to show that 

 sex is thus determined. There is no 

 manner of doubt that sex-production may 

 be affected by such conditions, and that its 

 operation may thus be in some cases arti- 



ficially altered. A classical example of 

 this is the fact, shown by the researches of 

 Prandtl, Buchtien, Klebs and others, that 

 alterations in the conditions of nutrition 

 or of light may determine the production 

 of the male and female organs in fern 

 prothallia; and analogous effects of 

 changed external conditions have been 

 produced in case of Hydra. But these are 

 not properly eases of sex-determination, 

 but rather of the suppression or retarda- 

 tion of one set of sexual organs in favor 

 of the other in hermaphrodites; and they 

 are not to be directly compared to a change 

 of sex in the true diecious forms. Again, 

 it has long been known that the production 

 of males in the aphids is definitely affected 

 by external conditions, and more recent ex- 

 periments show that the same is true of the 

 daphnids. But here again we are not 

 dealing with a change of sex in the indi- 

 vidual. These effects involve a change 

 from parthenogenetic generations that pro- 

 duce only females to those that produce 

 sexual females and males. The same is 

 true of Maupas's well-known results on 

 the rotifer Eydatina (though these have 

 been disputed). As far as ordinary 

 diecious forms are concerned most of the 

 recent experimental work, such as that of 

 Strasburger on the flowering plants, of the 

 Marchals on diecious mosses, of Schultze 

 and Cuenot on mammals, insects, amphibia 

 and other animals, has led to purely nega- 

 tive results, and seems to show that from 

 the fertilized egg onward the sex of the 

 individual is unalterable by external con- 

 ditions. 



n. SEXUAL PEEDETEEMINATION AND PRE- 

 DESTINATION IN THE GEEM-CELLS 



The whole mass of statistical and experi- 

 mental data on this question is placed in a 

 new light by the proof, recently brought 

 forward, that in many organisms the fer- 

 tilized egg or zygote is already prede- 



