80 
I take up this subject. I shall confine my attention to the form- 
ation of the anterior end of the duct. 
' The facts are very similar to those described by me in Amphibia !). 
I found, for example, in Salamandra atra a gradual extension of the 
cylindric epithelium of the pronephric nephrostomes, so that a con- 
tinuous plate of heightened cells results from the confluence of the 
perinephrostomial thickenings. This plate is more or less encroached 
on by the backward growth of a lateral connection between the ali- 
mentary tract and the body-wall; but it persists laterally and posterior 
to this connection, and gives rise to the anterior end of the Mül- 
lerian duct. A posterior thread-like prolongation of the plate passes 
outside the Wolffian duct, and is the first Anlage of a hinder part 
of the Müllerian duct. 
A crocodile of 10 mm in length (A) shows the Müllerian duct 
Anlage in a condition similar to what I described, not in my earliest 
stages of Salamandra, but in a salamander of 20 mm. The high 
cylindric epithelium of the pronephric funnels stretches in a continuous 
sheet between the nephrostomes and laterally over the pronephros 
region. It passes gradually into the ordinary low epithelium of the 
coelom, posterior to what I regard as the end of the pronephros; 
and it is not grooved or otherwise modified to form a tube. 
The next smallest crocodile (B) that is available for examination 
is 12 mm long. It is conspicuously further advanced in development. 
The degenerating, laterally-situated, anterior part of the embryonic 
kidney of the 10 mm specimen seems to have disappeared, and with 
it its nephrostomes; but still in front of the remainder of the 
embryonic excretory organ (mesonephros ?) ?) there is a distinct dorsal 
and lateral thickening of the coelomic epithelium. This was figured 
by WIEDERSHEIM; and Braun found a similar structure in Anguis 
fragilis, and speaks of it as „eine mir völlig unverständliche Ver- 
diekung“. This thickening can be traced back along the side of the 
coelomic diverticulum in which it begins. For the most part it is 
lateral, rather than dorsal as at first; and where the diverticulum 
joins the main division of the coelom, the lateral thickening runs far 
round ventrally. Through many sections it is a distinct plate lying 
immediately ventral to the junction of the mesonephros with the body 
1) Anat. Anzeiger, Bd. 9, 1894, and Trans. Roy. Soc. Edinb. 1896. 
2) There is some difficulty as to the exact limits of the pronephros 
and mesonephros. See WIEDEBSHEIN |. c. 
