THE GENERATIVE ORGANS. 141 



somites containing them persist as the generative tubes, and 

 become continuous behind with the twenty-first somite (PL 

 IX, figs. 42, 44), which does not divide into a dorsal and ventral 

 part but acquires a ventral opening in the same position as the 

 preceding somites. The opening soon, however, shifts to the 

 middle line, where it joins its fellow, so as to form the single 

 generative opening of the adult. In all probability the greater 

 part, if not all of the ducts of the adult, are derived from the 

 twenty-first somite ; the dorsal divisions of the five preceding 

 somites forming the generative glands only.' 



In Stage g the generative organs form two tubes lying in 

 the central compartment of the body cavity and closely applied 

 to one another in the middle line (PL IX, figs. 47, 48). 



I cannot say when the generative cells begin to show sexual 

 diiFerences. The appearance of the sections referred to (PI. 

 IX, figs. 47, 48) would lead one to suppose that the specimen 

 was a female, and I have but little doubt that it was. At the 

 same time, I must mention that I have never seen anything at 

 this stage which I could call a male. 



In January sexual differences are undoubtedly manifested by 

 the generative tubes. Those of the females presented very 

 much the appearance of the earlier stage. In the male the 

 nuclei were smaller and more numerous, and the lumen was 

 narrower. In fact, the organs differed very much in the same 

 way that they do in ripe embryos. PL XI, fig. 12, is from 

 a transverse section of a female embryo almost ready for birth, 

 and fig. 13 from a male embryo of the same age. At this 

 stage the ovarian tubes communicate with one another at their 

 extreme front ends, and behind where they pass into the ovi- 



' This view would be confirmed in the case of the female if it could 

 be proved that my suggestion (p. 97) that the receptaculum ovorum of 

 the neotropical species is part of the somite which gives rise to the genera- 

 tive opening and outer part of the generative ducts, and homologous with 

 the internal vesicle of the nephridia. The case of the male is more difficult, 

 but probably the testes (prostates of Moseley and Balfour) only, i. e. the 

 parts in front of the swollen vesiculse semiuales (testes of Moseley and 

 Balfour), are alone derived from the dorsal divisions of the generative somites- 



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