DEVELOPMENT OF DIGITIFORM GLAND 349 



tinuous. This arrangement of the entrance of the duct is such 

 that when the intestine is dilated the duct must be closed, 

 unless the pressure within the gland and duct is rather high. 



Blood supply. The digitiform artery arises from the aorta 

 anterior to the digitiform gland and courses obliquely ventrally 

 and posteriorly to the gland at or near to its distal extremity 

 (fig. 9). It has been called the posterior (inferior) mesenteric 

 artery by Parker ('87), and the posterior branch of the superior 

 mesenteric by Howes ('91). It may branch in the mesentery, 

 one ramus going anteriorly to the tip of the gland and the other 

 posteriorly along the dorsal surface. The anterior ramus may 

 be lacking. Numerous small rami are given off on either side 

 from the digitiform artery on the dorsal surface of the gland 

 (fig. 9). These surround the gland and anastomose on the ven- 

 tral side, where a ventral longitudinal artery may be formed. 

 Numerous capillaries from the surrounding arteries penetrate 

 the parenchyma, so that each tubule is in contact with one or 

 more blood vessels. These extend nearly to the central lumen 

 and gradually anastomose, forming venous sinuses which run 

 longitudinally along the lumen. The ventral sinus is the largest, 

 and the others enter it before the duct is reached. This sinus 

 (fig. 10) may be called the digitiform vein. It runs along the 

 digitiform duct and empties into the dorsal intestinal vein (fig. 

 IS). The blood supply is thus quite similar to that of the 

 mammalian suprarenal body which has an external arterial sup- 

 ply and an internal venous drainage system. The rich blood 

 supply suggests a secretory activity. 



Nerves 



The digitiform gland is well supplied with nerves (Monti '98). 

 A large trunk which appears to contain both medullated and non- 

 medullated fibers is present in the mesentery. It breaks up into 

 numerous rami which may be found within the capsule of the 

 gland. No ganglion cells were seen in any of the preparations 

 examined. The ultimate distribution of the nerve endings was 

 not made out because no special nerve stains were used. 



