BY WILLIAM A. IIASWELL, M.A., B.SC. 737 



There are two cfeca in the succeeding part of the alimentary 

 canal, each of which becomes branched, the branches themselves 

 showing a tendency to divide. The epithelium differs from that of 

 the gizzard in its much greater thickness, being composed of several 

 layers of cells, of which the superficial layer is ciliated ; the 

 epithelium of the caeca is looser and more irregular, and the cilia 

 appear to be absent. 



The only other noteworthy point in the structure of the 

 alimentaiy canal is the presence in the epithelium of the hinder 

 portion of the intestine of multitudes of greenish concretions 

 similar to those noticed by Claparede, in Syllis gracilis. 

 Precisely similar bodies occur, often in large quantities, in the 

 epithelium of the dorsal portion of the cseca of Folynoe and 

 Aphrodita, and they occur also abundantly in the narrow glands 

 of CJdoroima and the so-called tubiparous glands of Serpida and 

 Sahella. It is not unlikely that these concretions are in all these 

 cases of a uric character, and that the organ in which they occur 

 acts as the nephridium of the annelid. (1) 



The nerve-fibres of the ventral cord are arranged in three 

 distinct bundles, one smaller mesial, and two larger lateral. The 

 large ganglion-cells are grouped on the dorsal aspect of the ganglia. 

 Towards the middle line of the dorsal aspect of the cerebral 

 ganglia, is a group of very large ganglion-cells arranged in con- 

 verging lines enclosed in fibrous tissue, each group connected with 

 the fibrous matter of the ganglia by bands of fibres. External to 

 this, and nearly surrounding the whole of the fibrous matter of 

 the ganglia, is a layer of very small cells which form specially large 

 groups in the neighbourhood of the eyes. 



The eye has a homogeneous crystalline lens, apparently formed 

 of a thickening of the cuticle, a retina composed of short rod-like 

 elements which do not stain readily with hsematoxylin, and a layer 



(1) It is necessary to draw a clear line of distinction between the terins 

 "segmental organ" and "nephridium." Tlius the nephridia of Polynoe 

 are not the segmental organs, as Mr. A. G. Bourne maintains, but probably 

 the dorsal division of the intestinal caeca, the segmental organs being 

 generative ducts. 



