DEVELOPMENT OF DIGITIFORM GLAND 331 



the dorsal surface of the intestine, just posterior to the spiral 

 valve. He has since called my attention to the fact that it 

 appears as a hollow bud and is indicated in an embryo of 15 

 mm. as shown in figure 1 in the present paper. He traced its 

 growth through several stages to embryos of 37 mm. in length. 



KearneA^ ('14), working with Mustelus, stated that "the rela- 

 tive weight of the rectal gland appears variable in the embryo, 

 but falls from an average of 0.105 per cent to about 0.032 per 

 cent at birth. Shortly after birth the relative weight increases 

 slightly and thereafter decreases." 



Kellicott ('08) stated that at birth the relative weight of the 

 digitiform gland in Mustelus was found to be 0.0398 per cent 

 of the body-weight. He found no difference between sexes in 

 the weight of the gland in most cases. In 9 female and 9 male 

 specimens of Mustelus, averaging 73 cm. in length, examined 

 by the present writer, the digitiform gland of the females aver- 

 aged 23.5 mm. in length and in the males 22.5 mm. This differ- 

 ence is within normal variability. 



Blanchard ('78 a, '78 b) presents the first adequate histologi- 

 cal description of the digitiform gland, although Leydig ('52) 

 reported briefly on its microscopic structure, analogizing it 

 with the acinous glands of Briinner. According to Blanchard, 

 the gland in question shows the following characteristics. The 

 duct usually opens into the intestine in the mid dorsal line, 

 through an opening guarded by a fold of the mucosa. A sec- 

 tion through the middle of the gland shows the surrounding 

 connective tissue capsule which is continuous with a heavy sep- 

 tum which extends to the central lumen. The parenchyma is 

 not acinous but tubular, each tubule having many branches 

 which end in a culs-de-sac. The glandular tissue is lacking where 

 the duct joins the intestine. 



Pillet ('85) stated that the gland is covered by peritoneal 

 epithelium, under which are the round culs-de-sac of the tu- 

 bules which resemble the glands of Luberkuhn. The tubules are 

 lined with simple cuboid epithelium. Cell boundaries are in- 

 distinct. The large, centrally placed nuclei contain three or 

 four nucleoli. The cytoplasm consists of rather fine pale gran- 



