69 



» 

 nearly horizontal. At its upper extremity the coiling 



becomes rather irregular, and the tube passes into the 



succeeding coiled portion of the intestine near the axis of 



the latter. The crystalline style passes the opening of the 



spiral intestine, and its narrowed end is lodged in the 



short caecum already referred to. The anterior fold in 



the straight intestine continues on into the spiral portion, 



and passes into a thick pad, nearly filling up the lumen 



of the latter (T//., fig. 13, PL III.). This pad or typhlosole 



is formed by the same tissue which fills up the space in 



the anterior and posterior folds which divide the straight 



gut into right and left divisions. Owing to the presence 



of this typhlosole the spiral gut appears externally as a 



round tube, although in section the lumen is contracted 



and crescentric in form ; the tissue filling the typhlosole is 



continuous with a narrow layer surrounding the gut and 



with the general connective tissue of the viscero-pedal 



mass. 



After making about six turns the typhlosole disappears, 

 and the intestinal tube passes into a loose coil of four or 

 five turns, which may be described as the coiled portion 

 of the intestine {Al.c.5, figs. 3 and 11), and which lies 

 anterior to the spiral gut. The average diameter of this 

 coil is from 0*6 to 1 cm. Its most anterior turn joins the 

 spiral intestine ; its most posterior one passes off into the 

 rectum, which passes to the right side of the straight 

 intestine, and runs up along the posterior part of the 

 viscero-pedal mass {Al.c.6, figs. 3 and 11) to near the 

 dorsal portion of the latter, where it pierces the muscular 

 body -wall and enters the pericardium. After passing 

 through the ventricle of the heart, the rectum runs along 

 in the dorsal body-wall over the posterior adductor, and 

 terminates in the anus {An., fig. 3). 



The histologicml character of the epithelium of the intes- 



