THE URINOGENITAL SYSTEM 403 
day; retrogression begins immediately and is completed, or at 
any rate far advanced, on the eleventh day. In this process the 
epithelial wall disappears first, and its place is taken by cells 
of mesenchymatous appearance, though it is not known that 
transformation of one kind into the other takes place. Retro- 
gression begins posteriorly and proceeds in the direction of the 
head; the ostium is the last to disappear. The mesenchymatous 
tunic shares in the process, so that the ridge is no longer found 
(see Fig. 222). In the male the Miillerian ducts never open into 
the cloaca. 
In the female the development of the right Miillerian duct 
ceases after the eighth day, and it soon begins to degenerate. Its 
lumen disappears and it becomes relatively shorter, so that its 
anterior end appears to slip back along the Wolffian body. On 
the fifteenth day slight traces remain along its former course and 
a small cavity in the region of the cloaca. It never obtains an 
opening into the cloaca (Gasser.) 
With the degeneration of the anterior end of the Wolffian 
body the ostium tubz abdominale comes to be attached by a 
ligament to the body-wall (Fig. 231); farther back the ligamen- 
tous attachment is to the Wolffian body. 
The fimbriz begin to develop on the eighth day on both 
sides in both sexes. It is only in the left oviduct of the female, 
however, that development proceeds farther, and differentiation 
into ostium, glandular part, and shell gland takes place. This 
appears distinctly about the twelfth day. The lower end ex- 
pands to form the primordium of the shell-gland at this time, 
but does not open into the cloaca. Indeed, the opening is not 
established until after the hen is six months old (Gasser.) 
IV. THe SUPRARENAL CAPSULES 
The suprarenals of the hen are situated medial to the anterior 
lobe of the kidney, in the neighborhood of the gonad and vena 
cava inferior. They have a length of about 8-10 mm. The 
substance consists of two kinds of cords of cells, known respect- 
ively as cortical and medullary cords, irregularly intermingled; 
the so-called cortical cords make up the bulk of the substance, 
and the medullary cords occur in the meshes of the cortical cords. 
The terminology does not, therefore, describe well the topo- 
graphical arrangement of the components; it was derived from 
