294 T. H. Burvenp, 
factorily verified in some important particulars, in spite of ©. RaBr’s 
excellent work published in 1896. Although their statements are 
not all in complete agreement, yet the main results of these writers 
have tended to differentiate the Selachii from other Anamnia with 
respect to their kidney development, whereas from a comparative 
study of the development of other systems of organs we might 
reasonably expect the Selachian kidney to have a similar, though 
less complicated development than that found in most other Verte- 
brata. 
The metameric origin of the Selachian pronephros; the fusion 
of the distal ends of the first-formed tubules to produce a duct 
— the Sammelgang; the partly ectodermal origin of this duct; 
the nature of the vascular supply etc. are all important questions, 
requiring the most careful confirmation. 
The mode of origin and condition of the pronephros in a type 
like Scyllium unconsciously forms, in the mind of the evolutionist, 
a paradigm for the development in higher forms. Moreover, there 
are perhaps more diverse statements made by various workers in 
kidney ontogeny than have been made in respect of any other 
branch of comparative embryology. This may quite possibly be due 
to the fact that we have not yet reached the truth with regard to 
the development of the kidney in lower Vertebrates such as the 
Selachii. 
It was with a view partly of testing my own observations upon 
Chrysemys, partly to satisfy myself that the Selachii differ in im- 
portant respects in their kidney development from all higher and 
lower Vertebrates, and partly to give some observations upon a 
species of Scyllium not hitherto recorded in detail, viz. canicula, that 
I took up this matter. 
Throughout this inquiry I have been fortunate in obtaining the 
support and criticism of the late Professor Srpawick at the Royal 
College of Science, London. It was he who caused the requisite 
additional embryos to be sectioned and mounted under my super- 
vision, and with whom I had the privilege of discussing the results 
of this inquiry before his untimely death early in 1913. In addition 
to the embryos described below, I examined many other series of 
sections of Dogfish embryos in the Zoological Laboratory of the 
Royal College of Science, and these confirmed the results given 
below. Professor Sepawick was convinced that the kidney develop- 
