KIDNEY IN RELATION TO WOLFFIAN BODY IN THE CHICK, 63 



has been modified from part of the same primitive organ as 

 that from which the WolflSan body developed, as is the case 

 in the Icthyopsida ? 



To obtain an answer to these questions I have been 

 obliged to make a close study of the earliest stages in the 

 development of the kidney and Wolffian body. The results 

 obtained with regard to the latter are so different from 

 those obtained by the latest observers, that I have recorded 

 them in full in the following account. 



Peculiarities in the early development of the Avian 

 Woffian body necessitated an examination of the early de- 

 velopment of the Wolffian tubules in other Vertebrates. 

 This examination I was enabled to make in the case of 

 Elasmobranchii owing to the great kindness of Mr. Balfour, 

 who placed at my disposal the whole of his Elasmobranch sec- 

 tions. The result of this examination was to convince me that 

 the account given of the earliest stages in the development 

 of the Elasmobranch Wolffian body is in some respects 

 erroneous. 



Before proceeding to an account of the observations 

 made upon these heads it will be well to give a short 

 historical account of the progress of our knowledge on this 

 subject, i.e. the development of the Wolffian body and kidney. 



The later views as to the homologies of the parts of the 

 excretory system found in the different members of the 

 Vertebrate group dates from the work of Balfour^ and 

 Semper^ on the embryology of Elasmobranchs. 



The independent discoveries of these two investigators 

 gave an impulse to the study of the development of the 

 organs in question in other animals, and as a result it has 

 gradually become clearer as the embryology of more animals 

 became known that a great similarity in the development of 

 these organs characterised the Vertebrata. 



The earlier observers, Remak^ and Rathke,* maintained 

 that the tubules of the Wolffian body developed indepen- 

 dently of the Wolffian duct in a blastema of mesoblast cells 

 adjoining the inner side of the duct. 



Waldeyer, in his well-known work,^ asserted from his 

 observations, that the tubules of the Wolffian body developed 

 as outgrowths from the duct, and that the Malpighian bodies 

 arose independently in the adjoining mesoblast. The views 



^ ' Monograph on the Development of Elasmobranch Fishes.' 

 ' ' Urogenitalsystem der Plagiostomen. Arbeiten,' vol. ii. 

 ' ' Entwickelung der Wirbelthiere,' &c. 

 "* ' Entwickelungsgeschichte der Wirbelthiere,' Leipzig, 1861. 

 * ' Eierstock und Ei,' 1870, 



