82 
size, but from comparison with others I can say that it was consider- 
ably larger than 12 mm, and that probably it was less than 20 mm 
in length. 
Fig. 3. Section of same still further back, showing the beginning of the separation 
of the Müllerian duct Anlage from the lateral body-wall. 
Fig. 4. Section of same showing further stage in the cutting off of the Müllerian 
duct Anlage from the body-wall. 
Here, as in 5, the pronephros has degenerated. And here, too, 
for a considerable distance along the dorsal wall of each of the 
lateral diverticula of the coelom there is a distinct thickening of the 
epithelium. For the most part it is not spread over the lateral 
walls, but is a definite narrow band. Through a considerable number 
of sections it stands out in the diverticulum as a ridge. Anterior, 
however, to the beginning of the mesonephros the band extends 
laterally to form a plate. This continues along the body-wall in the 
front of the mesonephros region; but is not met with through many 
sections. In the first section through the mesonephros region on one 
side, and only a few sections further back on the other side, it is 
seen that the lateral plate is undermined by a new diverticulum of 
the coelom that projects forwards (d on right side of Fig. 5). About 
half a dozen sections further back this diverticulum ends; but one 
sees from remnants on the lateral wall (r Fig. 5) that it has extended 
further. By the breaking down of the ventral wall of this diverticulum 
the Müllerian duct Anlage, with its subjacent part of the lateral body- 
wall, is left connected chiefly with the mesonephros. There is no 
essential difference here from the mode of formation described in a 
