THE ANATOMY OF PENTASTOMUM TEHETTUSCULUM. 21 



composed partly of fibrous material and partly of cells. This 

 connective tissue is continuous with two mesenteries, one on 

 either side, which run off from the alimentary canal to the 

 hook-glands where these are present (fig. 16), and most pos- 

 teriorly behind the hook-glands pass off to the mid-dorsal 

 line (fig. 21). 



In two specimens the cells of the stomach wall differ from 

 those of the others examined, in containing a certain amount 

 of dark brown pigment. This is interesting since Macalister, 

 in P. imperatoris, describes the gland-cells as spheroidal, 

 deep brown in colour, and as giving the digestive canal a deep 

 hue rendering it visible through the body-wall.^ 



In his specimens from the lung of Boa imperator, Mac- 

 alister found the alimentary tract empty or nearly so. In P. 

 teretiu senium there are almost always present coagulated 

 remains of the blood on which the animal has been feeding. 



(5) Uectum or Hind Gut (fig. 59, H, G).— This forms a 

 short straight tube, which runs from the end of the mid-gut to 

 the very posterior extremity of the body. Its walls are rela- 

 tively thick, and the lumen small. Most internally lies a layer 

 of columnar epithelial cells, with a cuticular lining which is 

 directly continuous at the anus with that on the external sur- 

 face of the body. The cells dip down (fig. 59) under those of 

 the mid-gut. External to the epithelium is a thick layer of 

 connective tissue and longitudinal muscle-fibres [M. H. G.). 

 No trace of circular fibres can be seen. 



Embedded in the connective tissue around the part where 

 the hind and mid guts unite together, are a number of cells 

 exactly similar in structure to those which compose the hook, 

 head, and parietal glands. No trace of any duct leading away 

 from them can be detected {Al. GL). 



6. Secretory Organs. 

 (Figs. 6, 7, 29, 32, 51, 52.) 

 Perhaps the most striking feature in the anatomy of Penta- 

 s t o m u m is the great developm ent of glandular structures of an 



> Loc. cit., p. 62. 



