io6 POPULAR SCIENCE MONTHLY. 



fluence as that of the egg itself. It will be observed that there is a 

 certain catholicity in these conclusions at which Cuenot arrives, and 

 in the present uncertain state of our knowledge on many important 

 points it is probably wiser not to take too narrow a point of view in 

 regard to what factors determine the sex of the individual. 



Strasburger* has recently arrived at a somewhat similar conclusion 

 in regard to sex, basing his evidence mainly on certain observations 

 and experiments in higher plants. He, too, concludes that the sex of 

 the individual is determined in the egg, but he does not attempt to 

 push the question further than this general statement. 



Lenhossekf has also discussed in a more popular form the question 

 of the determination of sex, and he likewise urges that the sex of the 

 individual is determined in the egg. His discussion of the relative 

 number of males and females born in the human race is particularly 

 instructive, but it would carry us too far here to discuss the conclusions 

 at which he arrives. 



BornJ has carried out a series of experiments with mice, and finds 

 that the amount of food given to the parents produces no effect on the 

 relative numbers of males and females born. He also finds that the 

 age of the parents has no effect, nor has close interbreeding. He 

 arrives at the conclusion that the sex of the higher animals and plants 

 is determined in the egg.^ 



In striking contrast to the general conclusions of Cuenot, Stras- 

 burger, Lenhossek, and of Born there are two more recent theories in 

 which an attempt has been made to describe in detail how the sex 

 of the individual may be determined in the egg. Beard's paper, || 

 published in 1902, may be said, in a sense, to take up the problem 

 where it was left by Cuenot. He attempts to bring the problem of 

 the differentiation of the sexes into connection with the recent work 

 relating to the origin of the reproductive cells or gametes. Beard tries 

 to show that there are not only two kinds of eggs, but also two kinds 

 of spermatozoa that correspond to the two kinds of eggs. It is sup- 

 posed by him, however, that the determination of sex rests entirely 

 with the egg, and that the spermatozoa do not have any influence on 

 sex-determination. It is assumed, moreover, that one of the two 



* Biologisches Centralblatt, XX., 1900. 



t ' Das Problem der geschlechtsFestimmenden Ursachen,' Jena, 1903. 



t Sitz. phys. med. Gesell. WUrzhurg, 1902. 



§ Born points out that while it has been shown experimentally that in 

 hermaphroditic animals and plants, especially in the lower groups, it is possible 

 to cause one or the other kind of sexual organs to develop or to be suppressed, 

 that in the higher forms, at least in those in which the sexes are separated, it 

 has been found that the sex can not be changed by external factors. 



II Zoologische Jahrbiicher, XVI., October, 1902. 



