W. H. Coe — Anatomy of Cerehratuliis lacteus. 491 



(Plate XI, fig. 2, Plate XII, fig. 1, a?) is quite thin and is easily 

 broken by any sudden contraction of the muscular sheath; 



The Alimentary Canal. 



The alimentary canal may be divided into five principal regions : 

 mouth, CBSophagus, intestine, rectum and anus. 



The mouth is situated on the ventral side of the body a little 

 farther back than the posterior ends of the cephalic slits. It is capa- 

 ble of great variation in size and shape ; at one time appearing as a 

 small, round hole, and at another, as a longitudinal slit. The epithe- 

 lium of the mouth-opening is thrown up into numerous longitudinal 

 folds (Plate X, fig. 4) continuous with those of the oesophagus. It 

 passes insensibly into the epithelium of the integument on one side 

 and the oBSophagal epithelium on the other. There is an outer layer 

 of ciliated cells beneath which are large gland-cells in several layers. 

 Their granular contents stain with great intensity. There is a large 

 blood-vessel, the buccal, and a large nerve, the vagus, on each side 

 of the mouth. 



The oesophagus (Plate XI, figs. 1, 3) also has the epithelium 

 thrown up into great longitudinal folds but is entirely devoid 

 of diverticula. It is supplied with a loose musculature (fig. 1, m) 

 consisting of a few circular and longitudinal fibres ; there is also 

 a system of radial fibres connecting these muscles with those of 

 the circular layer in the body-wall. The oesophagus is surrounded 

 by a complex system of blood-vessels ramifying in all directions 

 beneath the epithelium. They are supplied from the lateral blood- 

 vessels and anastomose anteriorly with the buccal vessels. There is 

 a large number of these oesophagal vessels, as many as twenty being 

 seen in each cross section. In most related species the oesophagus is 

 surrounded by a comparatively small number of large lacunse instead 

 of contractile vessels as in this species.* In the nephridial region 

 the nephridial canals run parallel with the smaller blood-vessels. 

 The anterior portion of the oesophagus is innervated by the vagus 

 nerves, and the remainder by radial fibres from the nerve-plexus in 

 the body-wall. 



The epithelium (oe) is made up of a superficial layer of ciliated and 

 glandular cells and a deeper, thick mass of glands arranged in clus- 

 ters. There is also a thin layer of very large gland-cells situated 

 beneath the musculature. Each ciliated cell (fig. 5) is swollen near 



* Cf. C. Lexjdii, Plate XV, tig. 13. 



