464 SCIENCE PROGRESS 



of the organs proper to each sex to the other is remarkably 

 exhibited in the zebu, as can be seen in the pair of these animals 

 now in the Zoological Gardens. In the bull there are four 

 well-developed teats at the side of the scrotum, while in the cow 

 there is a vertical flap of skin resembling in form and position 

 the penis of the male. In Marsupials there is another instance 

 similar to that of the mammae : the pouch of these animals, 

 functional only in the female, is present in rudimentary form in 

 the male. These cases are in all respects similar to those in 

 which a male character is transmitted in rudimentary form to 

 the female ; for example, the spur and comb of the cock, the 

 horns of many ruminants, the elongated fin-rays of some fishes. 

 It is well known that the accessory organs of reproduction in 

 each sex are present in rudiment in the other. The clitoris in 

 the female is paralleled by the rudimentary uterus masculinus in 

 male mammals, and in lower Vertebrates rudimentary oviducts 

 are present in the male. 



So far we have considered only secondary characters, on 

 which the argument for the Mendelian theory is founded ; but 

 this is only indirect evidence of sex. The primary and essential 

 difference between male and female is that the former produces 

 spermatozoa, the latter ova. All other differences are secondary, 

 and there are numbers of species in which no other differences 

 exist. Considering that the fertilised ovum, or zygote, consists 

 of a spermatozoon and ovum united, it is difficult to understand 

 how it should be capable of giving rise to spermatozoa only, as 

 the Mendelian theory of sex supposes. The male is supposed to 

 be homozygous in sex; which means, if we leave the soma out of 

 consideration, that all the gametes descended from the fertilised 

 ovum are spermatozoa, and are incapable of transmitting the 

 power of producing ova. This would be to deny to half the ova 

 which are fertilised the property of heredity altogether with 

 respect to the cellular characters of the ovum itself. To say 

 that an ovum is male, means that it may contain all the characters 

 of the soma developed from it, but has no power to give rise 

 by simple cell-division to any other ova. I am inclined to 

 think that, even if the Mendelian theory were true, a male ovum 

 would be inconceivable in the present state of knowledge — quite 

 as inconceivable as is, according to the Mendelians, the heredity 

 of acquired characters. It is more important, however, to 

 consider whether the theory is in accordance with the evidence. 



