499 



condition, although the specialization of this group in many morpho- 

 logical features is readily conceded. 



I am much indebted to Professor W. N. Parker for his kindness 

 in placing at my disposal a valuable collection of embryos of Chelone 

 viridis (my das); to Professor A. Sedgwick, who readily gave me 

 permission to work in his laboratory, and to have access to an excellent 

 series of sections of Scyllium embryos; and also, to the Royal Society 

 for providing a grant which has enabled me to procure the 

 necessary embryonic material for the completion of the work. 



Historical. 



The development of the urinary organs of Chelonia has not 

 received the attention of many investigators, but van Wijhe ^ (1880), 

 MiTSüKURi^ (1888), WiEDERSHEiM (1890), and Gregory (1900) have 

 written papers which relate to the development of the kidney or its duct. 



MiTSUKURi dealt with the ectoblastic origin of the Wolffian duct: 

 Wiedersheim and Gregory paid special attention to the development 

 of the kidney. 



Wiedersheim's work dealt more particularly with Crocodilia, and 

 a brief comparison of the condition in Chelonia is given. He stated that a 

 pronephros is present in the embryo, and that this passes into the 

 mesonephros without break; that the pronephros degenerates at a 

 comparatively late embryonic period and only persists for a time as 

 a few glandular tubules which open into the front end of the coelom 

 by ciliated nephrostomes; that there is no segmentation of either 

 pronephros or glomus; that the glomus is richly folded, and extends 

 over more than four body segments, undergoing a complete atrophy 

 when- the Miillerian duct has opened into the cloaca; that, as in 

 other "Vertebrates, the pronephric duct becomes the mesonephric duct. 

 Wiedersheim was not able to state with certainty the number of 

 pronephric tubules, neither could he affirm whether the whole of the 

 urinary organ in the region of tlie glomus is pronephros. 



Gregory studied the development in Aromochelys and Platypeltis. 

 She concluded that heterodyuamous relations exist between pro- and 

 mesonephros, and also between glomus and glomeruli; that the 



1 I. W. TAN Wijhe, Urogenital-System bij de Schildpadden. (Nederl. Tijd- 

 schrift der Dierkundige Vereeniging Bd. V, 1880.) 



2 K. MiTSUKüRi, The ectoblastic origin of tlie Wolffian duct in Chelonia. 

 Zool. Anzeiger Jahrg. XI, 1888, Nr. 273. 



32* 



