454 ADAM SEDGWICK. 
Elasmobranchii) may be considered as in some respects primitive, 
the other must be regarded as very much modified. 
Whatever may have been the phylogenetic origin of the 
Wolffian tubules, the ontogenetic origin, as seen in Amphibia, 
Teleostei, Ganoids, Marsipobranchii, cannot possibly be re- 
garded as in any way approaching the former. We cannot 
suppose that a definite serial organ like the mesonephros de- 
veloped in phylogeny as a series of independent cavities in a 
mass of mesoblastic cells. At any rate, I think I am justified, 
in the present state of our knowledge, in making this statement. 
It is completely opposed to our ideas, and can only be accepted 
when all other hypothesis as to the origin of the mesonephros in 
phylogeny, based on the facts of embryology, have been shown 
to ‘be untenable. 
The tubules of the mesonephros in Hlasmobranchii, however, 
in which group they arise from parts of an organ previously 
developed, present a method of development which is not at all 
at variance with our @ priori views as to their phylogenetic 
origin. From considerations of this kind it seems to me a fair 
assumption that the development of the tubules in Hlasmo- 
branchs from parts of the body cavity more nearly resembles 
the method by which the organ arose in phylogeny than does 
that of the Wolffian tubules of the remaining Ichthyopsida. 
In Elasmobranchs the Wolffian tubules have a segmental 
arrangement; one is found in each segment. In all probability 
this also is a primitive condition. 
The arrangement of the tubules in the other vertebrata, 
although it does not actually afford support to this view, still it 
does not disprove it. It is a well-known fact that the segmental 
tubes have very rarely a segmental arrangement in the adult or 
even in theembryo. But in this connection it must be remembered 
that the tendency of development always seems to be to render 
that part of the mesonephros, which is going to function in the 
adult as an excretory organ, more compact, 7.e. to bring its 
constituent parts closer together. I need only refer to the kid- 
neys of the Urodele Amphibia. Here the posterior part of the 
mesonephros, which is going to function in the adult as kidney, 
becomes distinguished by its size and the course of its ducts 
from the anterior part, and in the female by its size only from 
the anterior part. And Fiurbringer has shown, in Salamandra 
maculata, that in correspondence with the increasing size of the 
posterior region there is found an increased number of primary 
tubules in a segment, as well as of dorsal secondary tubules.} 
1 Spengel however asserts, that in the female of those Amphibia he has 
investigated, the kidney (mesonephros) contains an uniform number of 
