THE HABITS AND STRUCTURE OP ARENICOLA MAUINA. 97 



with yellow glandular walls, extending from the level of the heart to 

 about that of the twelfth or thirteenth notopodium ; and (4) of an 

 intestine, of a dark brown or almost black colour, folded in a concertina- 

 like manner by the caudal septa, and opening at the terminal anus. 



During life the buccal mass (or " proboscis ") is constantly being 

 everted and withdrawn, carrying sand into the oesophagus. During 

 eversion several rows of curved, pointed, vascular papillae (B. Pop.) 

 are first extruded. These papillae (PI. VIII., Fig. 7) in old specimens 

 are tipped with chitin, and recall the armature of the proboscis in 

 certain Sipunculids {e.g. Phascolio/i collare 1 ). Then the more globular 

 portion of the buccal mass, covered with minute rounded processes, is 

 protruded. Finally, when fully everted, the buccal aperture is 

 surrounded by a few pointed pigmented jDapillse, which are continuous 

 with the lining of the first part of the oesophagus. 



The oesophagus 2 itself is slightly looped behind the second diaphragm. 

 It is a thin-walled distensible tube, the first part of which is lined by non- 

 ciliated mucus-forming cells. The middle portion is lined by a cutiile, 

 and the posterior part by cells resembling those of the stomach in bearing 

 cilia. The oesophageal pouches (Oe. Gl.) are somewhat flask-shaped, and 

 open into the cavity of the oesophagus by a short tubular stalk. They 

 are usually greenish in colour, but have a slight reddish tinge on account 

 of their very large blood-supply. Their blood-vessels are connected with 

 the lateral oesophageal and dorsal vessels. The cavity of the pouch is 

 subdivided by twenty-five to thirty incomplete partitions, produced by in- 

 folding of the wall of the pouch, and therefore covered on each side by 

 the epithelial lining of the pouch (PI. IX., Fig. 22). Between the 

 epithelial lamelhe is a blood-sinus, which is slightly enlarged at the 

 inner end and slightly thickened at the edge of each partition. The 

 oesophageal pouches are lined by ciliated epithelium, covered with a 

 fairly stout cuticle, and contain glandular cells. The walls of 

 the oesophagus are marked by longitudinal 'and circular muscular 

 impressions. 



The stomach, marked out by the patches of yellow tissue on its 

 walls, extends from the level of the heart to about the twelfth notopodial 

 setae. As we have already stated (p. 94), the stomach is bent upon 



1 Selenka, 'Die Sipunculiden,' 1883, pi. vi., fig. 74. 



2 The histology of the alimentary canal has been carefully investigated by 

 Wiren (1887, p. 31). Our results agree very closely with his. 



