DEVELOPMENT OF DIGITIFORM GLAND 335 



are nearly cuboid in form. Some of the primary tubules have 

 begun to form tubules of the second order. 



In a 47.5 mm. embryo (fig. 25), the external surface of the 

 (entodermal) digitiform gland has undergone considerable 

 change. The general shape is still cylindrical with narrowed 

 extremities. The duct has decreased in diameter, but is of 

 greater length. It extends posteriorly and laterally for nearly 

 a millimeter, and curves around a bend in the intestine in its 

 lateral course. The ostium of the duct is about the same dis- 

 tance from the spiral valve as in the 22.5 mm. embryo, although 

 the intestine has nearly doubled its length in this region. The 

 diameter of the gland is about twice that of the 33.1 mm. em- 

 bryo, and the number of tubules has more than doubled. The 

 newly formed primary tubules (fig. 29) are much smaller than 

 those of the 28.1 mm. stage (fig. 27). Many of the original 

 primary tubules are still large and unbranched, but others 

 have branched in various directions, forming secondary tubules 

 of various shapes and sizes. This branching is dichotomous 

 in places, but also there are clumps of small tubules of the second 

 order formed from a single tubule of the first order. 



In the embryo 95 mm. long (fig. 26) the digitiform gland and 

 duct together are about 6.6 mm. in length. The duct is about 

 1.5 mm. long and extends from the gland in an oblique plane, 

 running backward for a short distance, then turning sharply 

 away from the intestine. Almost the entire duct is embedded 

 within the wall of the mesenchyma of the intestine. Its end, 

 which is solid, joins a solid ridge of the gut (fig. 13). The lumen 

 of the duct and intestine are continuous through a lateral slit- 

 like opening in the duct (fig. 14). The internal surface 

 of the gland is very irregular, owing to the development 

 of a large number of tubules (fig. 30) . As many as fifty tubules 

 may appear at the periphery in a single transverse section of 

 the gland. These extend radially from the longitudinal axis 

 and nearly at right angles to it, although some are turned to- 

 ward the proximal end of the gland. Some of the primary 

 tubules are more or less isolated from the others, but many 

 tubules are grouped in somewhat cone-shaped clusters, the 



