498 • 



dealing with the early development of the urinary organs of the 

 Chick. 



The writer's attention was first directed to this subject whilst 

 examining some sections of rather late embryos of Chelone viridis, — 

 in which the condition of the anterior end of the kidney is such, 

 that WiEDEKSHEiM, ^ in 1890, stated that Chelonia agree with Crocodilia 

 in having a well-developed pronephros persisting until a comparatively 

 late period in their ontogeny. More recent work by Miss E. K. 

 Gregory^ has not apparently borne out the conclusions reached by 

 WiEDERSHEiM, it being suggested that Wiedersheim's earliest embryos 

 were already too old to permit of a successful study of the phylogenetic 

 changes which the anterior end of the kidney in Chelonia undergoes. 

 Since 1900 there has been no further attempt to elucidate the prob- 

 lem, so far as the writer is aware, and it was felt that progress in 

 this matter might help towards a solution of some of the complex- 

 ities at present prevailing with regard to the relations which exist 

 between pronephros and mesonephros; whether we ought to look 

 upon these structures as homodynamous, and, if so, by what changes 

 and under what impulses has evolution from pronephros to meso- 

 nephros occurred; or, again, if heterodynamous relations exist between 

 pro- and mesonephros, under Avhat conditions has the pronephros 

 given place to the mesonephros. That the problem is an intricate 

 one is shown by the amount of literature on the subject Avhich has 

 appeared within the last thirty years, — for a recent account of which 

 the reader is referred to the excellent summary of Felix ^. 



The only excuse which I can offer for attempting the solution of a 

 matter which has so far defied satisfactory explanation, and upon 

 which the best authorities are by no means unanimous, is that I 

 have for some time held the view that in respect of their kidney 

 development, at least, the Chelonia exhibit a remarkably primitive 



1 R. WiEDERSHEiM, Über die Entwickelving des Urogenitalapparates bei 

 Crocodilen und Schildkröten. Anat. Anzeiger V. Jahrg. 1890, Nr. 12. 



Ibid., Archiv für Mikr. Anat. Bd. XXXVI 1890. 



2 E. R. Gregory, Development of Excretory System in Turtles. Zool. 

 Jahrb. Bd. XIII, 1900. 



3 W. Felix, Die Entwickelung des Harnapparates, im Handbuch der 

 vergl. und exper. Entwickelungslehre der Wirbeltiere (herausgegeben von 

 Dr. 0. Hertwig., Bd. lU, Jena 1906). 



