PHYSIOLOGICAL VIEW OF THE PROBLEM 481 



even the larvae (tadpoles) remained for a time undecided. In 

 this connection, it should be remembered that there is strong 

 evidence showing that the hagfish {Jslyxine glulinosa) is for a 

 time distinctively male, producing spermatozoa, and that it 

 afterwards becomes as distinctively female, producing only 

 ova (Cunningham, Nansen). 



Among Invertebrates, the sexual organs are often late in 

 acquiring definiteness in favour of either sex — that is, the 

 period of sexual neutrality or indifference is prolonged. 



It seems as if, the higher the organism is in the series, the 

 earlier is its sexual destiny sealed. 



What Sex primarily means. — In the simplest cases, which 

 should be considered first, the ovum developing into a female 

 differs from an ovum developing into a male only in this— that 

 the one contains the dominant potentiality of an ovary, while 

 the other contains the dominant potentiality of a testis. This 

 appears to us to be a purely physiological difference, a slight 

 difference in the equation of metabolism, a slight difference in 

 protoplasmic gearing, quite comparable to that between an 

 active and a sluggish cell. In more complex cases, where there 

 is marked difference between the sexes as regards the gonads 

 themselves, the genital ducts, the external genital organs, and 

 secondary sexual characters, we suppose that there are definite 

 determinants gradually established and elaborated to correspond 

 to these organs, that these are equally present for both sexes 

 in all ova and in all sperms, and that their liberation or latency 

 depends on the bias towards egg-production or sperm-production, 

 by hypothesis a difference in physiological gearing. 



When we consider the very marked and detailed contrasts 

 between the sexes which are familiar in many birds and mammals, 

 insects and crustaceans, and so on, it may seem idle to refer 

 this to a primary difference in " physiological gearing." But our 

 familiarity with these secondary sexual characters is apt to lead 

 us away from the main problem, which is better studied in 



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