5 I 2 /• PERCY MOORE. [Vol. X. 



the ends of the radial muscle fibres (Big. \\, ep). If the epi- 

 thelium could be completely isolated, it would present somewhat 

 the appearance, without the regularity of pattern, of those 

 ingenious rubber change mats which are in such frequent use 

 on the show-cases of our stores. 



Immediately external to the epithelium and highly developed 

 is a continuous layer of circular muscles. The fibres have a 

 very regular arrangement (Fig. 9, ep), are completely tubular, 

 and increase in size toward the posterior end of the head, 

 where they pile up into several layers and pass into the pos- 

 terior cephalic septum, behind which they rapidly diminish into 

 the delicate muscular coat of the oesophagus. 



Radiating on all sides from the pharyngeal walls, traversing 

 the head cavity and passing into its outer walls, are numerous 

 large isolated muscle fibres (Figs. 9 and 11, vm). These origi- 

 nate externally from the longitudinal muscles, become somewhat 

 constricted within the head cavity, and break up at their inner 

 ends into numerous branches which spread and straddle the 

 circular fibres, passing between them and penetrating the 

 pharyngeal epithelium as described above. They are among 

 the largest muscular fibres of the body, reaching a diameter 

 of .025 mm. The central granular protoplasm is well marked, 

 and contains a conspicuous nucleus, which may, however, lie 

 on the exterior of the fibrillated protoplasm (Fig. 11, rm^). A 

 pair of small, berry-shaped glands are attached, one on each 

 side, to the lateral angles of the pharynx, just behind the jaw 

 pads. They are partially indicated in Fig. 10, g. 



The oesophagus is short, and its posterior limit rather ill 

 defined. It is characterized by a sudden diminution of mus- 

 cular tissue in the walls of the digestive tract, which takes 

 place after penetrating the posterior cephalic septum and enter- 

 ing the first body somite, by a change in the character of its 

 lining epithelium, and by the absence of chloragogue cells, 

 which distinguish the intestine. The alimentary canal begins 

 to increase in diameter within the body segments, and exhibits 

 a slight sacculation in the second. In this region the lining 

 epithelium is a single stratum of columnar cells, with freely 

 rounded and often bulbous, projecting ends (Fig. 7, oe). No 



