274 --BRNEST W. MACBRIDE. 
The method employed was exclusively that of series of 
transverse sections. The air contained in the lungs proved a 
great nuisance; and it was found advisable to open the frogs 
and remove the greater part of the gut, almost all the liver, 
the heart, and most of the lungs. Care had, however, to be 
exercised not to disturb the proximal parts of the liver and 
lungs, owing to the peculiar relation of the abdominal open- 
ing of the oviduct to them. (Vide infra.) 
It will be best to commence the accouat of the development 
with a short summary of previous work on the subject. Fiir- 
brenger’s classic research on the Salamander (‘ Entwicke- 
lungsgeschichte der Amphibien-Niere,’ Heidelberg, 1877), is 
well known. He asserts that the oviduct arises as an involu- 
tion of the peritoneal epithelium behind the pronephros, which 
applies itself to the Wolffian duct, and grows back as a rod of 
cells split off from the latter (quoted in ‘ Balfour’s Compara- 
tive Embryology,’ p. 710). Hoffmann, in the ‘ Zeitschrift fiir 
wissenschaftliche Zoologie,’ Bd. xliv, 1886, gives a somewhat 
similar account for the Frog. He finds that the oviduct arises 
from a patch of modified peritoneum just ventral to the third 
and now only remaining nephrostome of the pronephros. 
This patch, he says, is dorsally involuted to form a groove, 
open below. Ventrally it is prolonged downwards and out- 
wards over the surface of the pronephros, and even beyond it 
for a short distance. It is distinguished from the unmodified 
epithelium by being highly columnar. The part of the Wolff- 
jan duct in front of the mesonephros, the lumen of which is 
at this stage much reduced, then separates itself from the de- 
generating pronephros, and splits into two rods of cells. The 
dorsal of these is continuous with the Wolffian duct behind, 
and the ventral one applies itself in front to this involuted 
patch of peritoneum, and forms the first rudiment of the ovi- 
duct: But the oviduct does not grow back in continuity with 
the Wolffian duct. On the contrary, it enters into close con- 
nection with a longitudinal strip of peritoneum which lies to 
the outer border of the kidney, and consists of columnar epi- 
thelium. Hoffmann states that the hinder portion of the duct 
