10 "TERRA NOVA" EXPEDITION. 



which there is a single pair (Fig. 1, Sp.), are placed far forward, just in front of the 

 septum separating segments IV. and V. 



INTERNAL ANATOMY. 



Alimentary Canal. The mouth is on the ventral side, and is, as usual, over- 

 hung by the prostomium. It leads into a narrow buccal cavity, whose only 

 peculiarity is the presence of a small, pointed, tongue-like organ on its floor. This 

 "tongue" (Fig. 12, T) lies with its point directed backwards, after the manner of 

 the tongue of a frog. Its point is almost hair-like, and the organ is probably 

 sensory in function. 



The buccal cavity is succeeded by a pharynx, whose roof is formed by a very 

 thick muscular pad, provided with strong retractor muscles (Figs. 1 and 12, MPh.). 

 The whole pharynx, with its muscular pad, appears to be capable of eversiou, some 

 of the preserved worms having been found in this position. In this case, the little 

 'tongue" on the floor of the buccal cavity is probably also carried to the exterior, 

 and may there come into use as a feeler or gustatory organ. 



Just behind the muscular pad of the pharynx the oesophagus commences, and 

 at this point, on the dorsal side, there open into it side by side a pair of short 

 blind tubular organs (Fig. 12, Sal.), which may be the so-called " salivary glands." 



Further back, on either side of the oesophagus there are three glandular masses, 

 the " septal glands" (Figs. 1, 10, 11 and 12, Sep.); the first pair attached to the 

 anterior surface of the septum between segment IV. and V., and the second and third 

 pairs attached in a similar manner to the two following septa. The glands thus 

 occupy segments IV., V. and VI. ; they are massive and solid, and are L-shaped, 

 each having a dorsal prolongation. They are not, however, continuous over the dorsal 

 side of the oesophagus. This portion of the alimentary canal is richly lined with 

 long cilia (Figs. 10 and 11, Oes). Behind it the intestine is continued without any 

 marked increase in diameter, and passes down the whole length of the worm to the 

 anus, which is terminal. 



Circulatory System. The main reservoir of blood seems to be a large blood- 

 sinus which surrounds the gut, and is most conspicuous (in sections) in the region 

 of the oesophagus (Fig. 11, B S). 



In addition to this there is the usual system of vessels characteristic of the 

 Enchytrseidse (Fig. 5). The dorsal vessel (DV) takes its origin at a point on the 

 wall of the intestine at the septum between segments XIII. and XIV. Passing 

 forwards just above the gut, it bifurcates in the first segment, forming the usual pair 

 of lateral vessels (LV), which pass round the pharynx and join just behind it on the 

 ventral side, to form the ventral longitudinal vessel (VV). The dorsal and lateral 

 vessels are connected also by two pairs of conimissural vessels (C, C'), which arise 

 from the dorsal vessel close together in the fourth segment. The anterior pair pass 

 forwards and round the pharynx to join the lateral branches a little behind their 



