532 



THE AMERICAN NATURALIST [Vol. LV 



and only the simple peritoneal epithelium remains (Fig. 

 5). 



Shortly after this migration the canaliculi seminalis 

 are formed, at first as irregular slits, but already during 

 metamorphosis they develop into characteristic radiating 

 tubes. At all times they remain connected with the sex 

 cords. These on their part give rise to the rete vasculo- 

 sum Ilalleri and the connections with the mesonephros 

 (Vasa efferentia testis).^ 



In the following years the testes grow very slowly until 

 the fourth season, when a rapid increase due to active 

 mitotic divisions of the spermatogonia begins. The sper- 

 matic tubes become convoluted; spermatocysts are 

 formed and in the month of July the maturation cycle 

 begins. In August and September the spermatozoa are 

 developed. 



In only one case have I found an abortive priesperma- 

 togenesis in a three-year-old grass frog {R. temporaria) . 

 But as Clianipy has observed, similar degenerating mat- 

 uration cycles are fro(iueiitly formed in water frogs {R. 

 esculenta) in {lie second year. According to Swingle 

 precocioii- riix jiin- dt male germ cells in the bull frog 

 {R. catr^h- nil n) ;ilic;i(ly occurs in first year larva^, and 

 ripe sjxM jnarozon nrc formed in second year animals. 



Chardi Icrislivs: ], Central germinal. layer. 2. First 

 ripening stages ginng rise to functional spermatozoa in 

 the fourth season. 3. The maturation divisions directly 

 siiereed file pseiidorediicfional stages. (There is no sec- 

 <ui<l urowtli iM'i-i(»(l.) 4. Rete apparatus and Vasa effer- 



4. llrninijtJnod'iyiH. It is a strange and interesting 

 fact that the tNpical development of the testis as just 

 descriltcl !■> iarcl\ oh^'rved. Under natural conditions 

 most iiidiv i(lual< dcNclop first ovaries which later on 

 are traTisroi-iiicd into testes. During this transforma- 

 tion the gonads, showing the characteristics of both sexes, 

 are hermaphroditic; but without exception the female 



