SEPARATION OF THE SEXES. 



101 



hermaphrodite arrangement ; such, for instance, as may be seen in 

 the arrangement of the generative ducts of the Vertebrata. In the 

 Amphibia both male and female generative ducts, which are secondarily 

 derived from the urinary ducts, are developed in each individual. 

 The oviduct (Mullerian duct) in the male atrophies, and is only repre- 

 sented by a small rudiment (fig. 96&, Mg] \ while, on the contrary, 

 in the female, the vas deferens (Wolffian duct) is rudimentary, or, 

 as in Amphibia, functions as the efferent duct for the kidney secre- 

 tion (fig. 96a, kg). 



With the separation of the male 

 and female gene- 

 rative organs in 

 different indivi- 

 duals the most 

 complete form of 

 sexual reproduc- 

 tion, so far as con- 

 cerns division of 

 labour, is reached ; 

 but at the same 

 time a progressing 

 dimorphism of the 

 male and female 

 individuals be- 

 comes apparent. 

 This is due to the 

 fact that the or- 

 ganization in bi- 

 sexual animals is 

 more and more 

 influenced by the 

 deviating func- 

 tions of the sexual 

 organs, and with the increasing 



complication of sexual life becomes modified for the performance 

 of special accessory functions connected with the production of ova 

 and spermatozoa. 



In the first place, the modification of the generative ducts of the 

 two sexes in accordance with the function they have to perform 

 determines the development of secondary sexual characters and of 

 sexual dimorphism. Other organs as well as the generative appa- 



FIG. 94. Generative appara- 

 tus of a rhabdocoele Tur- 

 bellarian (Vortex viridis) 

 (after M. Schultze). T, tes- 

 tis ; Vd, vas deferens ; Vs, 

 seminal vesicle; P, pro- 

 trusible penis; Ov, ovary; 

 Va, vagina ; M, uterus ; 

 -D, yolk gland ; Rs, recep- 

 taculum seminis. 



FIG. 95. Generative appa- 

 ratus of the medicinal 

 leech, T, testis ; Vd, vas 

 deferens; Nh, vesicula 

 seminalis ; Pr, prostate ; 

 C, penis ; Ov, ovaries 

 with vagina and female 

 generative opening. 



