i88 



CARL L. HUBBS. 



cytologically at earlier stages than this, although he traced the 

 development of the sex-cells from much smaller embryos. 



At the 15 mm. stage the sexual differences in the form of the 

 anal fin are also apparent in Amphigonoptenis and Micrometrus, 

 although the gonad remains merely a fine strand of tissue ; but at 

 the 20 mm. stage the testes have begun to enlarge, and a slight 

 thickening of the radial membranes marks the position of the 



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FIG. 3. Section of testis of a newly-born Amphigonoptenis, showing several 



stages in spermatogenesis. 



elaborate gland developed later on the anal fin of the male. The 

 development of these primary and secondary sexual structures 

 thence rapidly proceeds in Amphigonoptenis aurora until birth, 

 at which time the gland on the anal fin is fully elaborated (see 

 Fig. 2), and all stages in spermatogenesis from the primordial 

 germ cells to transforming spermatids at least are evident in the 

 testis, the spermatogonia predominating. Just after birth, the 



