IB 



of the luitl-g-ut to the po.sterioi' ciul. On the dorsal side of 

 the anterioi' region, in the median line, a typhlosole {t.y.) 

 is foi lued hy tlie floor of a groove beiug" re-invagiuated ; 

 posteriorly, the sides of the groove widen out into an 

 elongate spoon-shaped structure. The function of the 

 ty])hlosole is ])rohably not, as is usual, to assist in the 

 absorption of food, but to provide a channel along whi(di the 

 secretion of the hepatopancreas is able to flow to the middle 

 region of the intestine, hi tlie middle region of the mid- 

 gut the epithelial cells exhibit a very regular arrangement. 

 They are arranged in double roAvs, which run out in an 

 oblique direction from the median line. The rows of cells 

 pi-oject into the body cavity, so that grooves are formed 

 between the double rows. In these grooves the muscle 

 fibres are lodged, underneath the blood-vessels from the 

 intestinal arteries. The posterior region is marked by the 

 presence of the sphincter muscle, which separates the mid- 

 gut from the rectum. In the sphinctal region the faeoal 

 pellets are formed. 



The rectum is a short uniform tube o])ening by the 

 longitudinal slit-like anus. 



The salivary glands. There are two pairs of salivary 

 glands situated in the cephalon, on each side of, and 

 opening into, the oesophagus. Each is made up of 

 a large number of rosette-like masses of gland cells, Avhich 

 are very similar to the mucous glands described by Allen 

 (1892) in Ft/laemonefes. In section, they have the 

 appearance shown in the figure (PI. II., tig. 17). Each 

 acinus is made u]) of a number of concentric 

 cells, in which two regions can be recognised — a peripheral 

 cytoplasmic region containing the nucleus, and a central 

 glandular region. Each of the cells lias at' its internal 

 apex an intracellular duct (ic.d.), whicli opens into a duct 

 common to the mass of cells [cd.). This duct is probably 



