276 ERNEST W. MACBRIDE. 
pointed in expecting a stage of development corresponding 
to these external marks. 
My next stage is the earliest in which any trace of the duct 
is visible. The animal is truly a frog, having lost the peculiar 
tadpole mouth, and having both pairs of limbs well developed, 
but the tail is just commencing to be absorbed (total length 
38 mm., tail 21 mm., in one specimen ; in another, total length, 
19 mm., tail4 mm.; both show same features). One nephro- 
stome only remains (pz. f., fig. 1); but, as this is situated some 
considerable distance in front of the glomerulus, it must be 
regarded as the first, and not the third, of the preceding stage. 
Immediately ventral to it there is a groove in the peritoneum 
open below, the epithelium of which is highly columnar, and 
stains much more deeply than that of the nephrostome (m/f, 
fig. 1). This columnar epithelium is continued out over the 
surface of the pronephros and beyond it, as Hoffmann has de- 
scribed (C. p. e., fig. 1). This groove, traced backwards for fifteen 
sections, becomes a canal, which, after two sections, ends in a 
solid thickening of the peritoneum (Md., fig. 2). In the next 
stage only a rudiment of the tail remains, but the condition of 
the funnel is exactly the same, except that there is an indica- 
tion of the groove running ventrally, described by Hoffmann 
(Vg., fig. 3). In both the preceding stages traces of the almost 
atrophied pronephric tubules are still visible (pn. t., figs. 2 
and 3). 
In the next two stages the tail has completely vanished. In 
the first of these the groove formed from the columnar epithe- 
lium is very distinct, but still open (fig. 5, 4). In the second 
it has closed to form a canal, so that the abdominal opening is 
carried ventralwards round the base of the lung, and at the 
same time backwards. It does not, therefore, appear as before 
in the same section as the groove, which latter is now an addi- 
tional piece of the oviduct ; consequently it appears in the same 
section as a more posterior part of the duct (Md. and mf., fig. 
6 6). It is closely attached to the ventral surface of the liver, 
and runs back along it, gradually shallowing out. Traces also 
of the fimbrize of the adult orifice can beseen. I have examined 
