BY WILLI1.M A. HASWELL, M.A., B.SC. 2Go 



The Intestinal Cmca. 



These correspond in number with the segments, except that 

 some of the anterior segments are commonly devoid of them, and 

 a few of the posterior cnoca are usually rudimentary. On account 

 of the presence of the elongated gizzard, the caeca corresponding 

 to the anterior segments are connected with the front portion of 

 the intestine by greatly elongated necks, and thus assume a 

 different form from that displayed by the rest. Taking one of 

 the cceca from the middle of the intestine we find it to consist 

 (1) of a narrow neck, (2) of a dorsal portion, and (3) of a ventral 

 portion. The neck communicates with the cavity of the intestine 

 by a funnel-like aperture, immediately around which the intestinal 

 cilia are much longer than elsewhere. It is ciliated internally, 

 and is subject to peristaltic contractions synchronous with those 

 of the dorsal portion of the caeca. In structure its walls resemble 

 those of the intestine. The neck leads into the dorsal portion of 

 the caecum, which winds round behind the dorsal muscles, and 

 ends in close relation to the dorsal integument. From this opens 

 the ventral portion, which bends downwards towards the ventral 

 body- wall. This ventral portion is never branched ; its walls are 

 similar to those of the intestine, and it is usually found to be 

 distended with opaque matter — evidently food undergoing the 

 process of digestion. The dorsal portion is in some genera 

 fAphrodita and Iphione) complexly branched — the terminal 

 branches being lodged in the interior of the scale tubercles and 

 the bases of the dorsal cirri. In other forms {Thormora), it is 

 simply divided into two or three branches, and in others {Polynoe)^ 

 it is practically undivided, presenting merely irregular elevations^ 

 (pi. vi., fig. 1.) 



When simple and sac-like the dorsal caecum is divided internally 

 by incomplete septa, which are prolongations inwards of the wall 

 of the caecum, consisting of muscular and connective tissue, with 

 a few spindle-shaped nuclei. The interior of the caecum is lined 

 here and there with " hepatic cells." These are large spherical 



