KIDNEY IN RELATION TO WOLFFIAN BODY IN THE CHICK, 147 
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 
of other observers, before 1874, were identical with one or 
the other of these. 
* ‘ Monograph on the Development of Elasmobranch Fishes.’ 
’ ‘ Urogenitalsystem der Plagiostomen Arbeiten/ vol. ii. 
’ * Entwickelung der Wirbelthiere,’ &c. 
* ‘ Entwickelungsgeschichte der Wirbelthiere,’ Leipzig, 18 G 1 . 
‘ ‘ Eierstock und Ei,’ 1870 . 
