DEVELOPMENT OF DIGITIFORM GLAND 341 



cytoplasm. In the older, central part of the gland the cells are 

 columnar and contain oval nuclei, and relatively more cytoplasm. 

 The lumen of the gland is narrow, even slit like in places, owing 

 to the fact that the entire wall is involved in the tubule formation. 

 The surrounding mesenchymal and peritoneal cells are rather 

 flat, with oval nuclei. There is no certain differentiation of 

 smooth muscle. The proximal portion of the gland is lined with 

 columnar epithelium showing two to four layers of nuclei. 



Still greater changes are to be seen in the 33.1 mm. stage 

 (fig. 4). The number of tubules of both the first and second 

 orders has greatly increased. The main wall of the gland is 

 thinner than before and contains relatively fewer and smaller 

 nuclei. In most places, not only in the tubules but also in the 

 wall of the main lumen, there is but a single layer of cells. As 

 noted before, the younger nuclei are round and the older arc 

 oval in outline. The lumen of the gland is irregular an its 

 inner surface is much pitted. The proximal portion (duct) of 

 the gland is lined with an epithelium which is narrower than in 

 previous stages. It consists of but one or two layers of colum- 

 nar cells with oval nuclei. The outer mesencyhmal cells show 

 fibril formation and their nuclei are flattened and elongated. 

 The mesothelial outer covering is quite thin. 



Few cellular changes are to be seen in the digit if orm gland 

 of the 47.5 mm. embryo (fig. 5) except that the epithelium is 

 thinner and the nuclei are relatively smaller. The surround- 

 ing mesenchyma and mesothelium have become more compact. 

 Numerous new tubules have formed, but, in finer structure, 

 they do not differ from those already described. Vascular 

 channels are numerous. The lumen of the gland is relatively 

 large. The duct is lined with high columnar cells. 



In the 95 mm. embryo (figs. 6 and 8), the columnar epithelial 

 cells in the tubules, as well as in the wall of the lumen, are rela- 

 tively larger and contain smaller and fewer nuclei. The newly 

 formed tubules of the third and fourth order are of about the 

 same diameter as those from which they have arisen, except 

 at the distal ends which are narrower. Both connective tissue 

 and smooth muscle nuclei may be made out in the proximal 



