52 Prof. M'lntosh's Notes from the 



of numerous longitudinal blood-vessels and a large dorsal 

 vessel, whereas the larger stomachal area, with its firm and 

 thick walls and its centra] vertical slit, has externally a 

 blood-sinus all round, and no separate dorsal vessel is now 

 apparent. The narrower anterior region, therefore, with its 

 numerous longitudinal vessels, may differ in function from 

 the wider posterior region surrounded by a blood-sinus. 



The enlarged region, with its thick walls, continues beyond 

 the posterior termination of the thoracic glands — that is, 

 after the formation of the ventral longitudinal muscles — and 

 behind this where the body-wall is wider and more flattened. 

 Food is more frequently present in the anterior part than 

 in the wider posterior region. In the narrower part of the 

 body, behind the foregoing, where the muscles become pro- 

 portionally massive, the walls of the intestine are much 

 folded and the area is large, but the structure of the wall is 

 the same, though little cellular tissue surrounds the vascular 

 sinus externally. Still further back the gut dilates into a 

 wide chamber without folds and having the vascular sinus 

 externally. Then it thickens laterally, apparently from a 

 septum-like fold with a vertical V-shaped slit in the centre, 

 the upper and lower arches being thin. Thereafter the firm 

 and rather thick-walled canal shows a median pair of plates 

 in section*, as if from a fold or valve (PI. V. fig. 31), and 

 then, proceeding backward, enlarges so as to form the two 

 halves of a pear which fill up the entire central area, a slit 

 soon appearing in the middle of each half, and finally 

 broadening out into a T-shaped fold, which runs from the 

 transverse dorsal folds by a long median one to the ventral 

 wall (PI. V. fig. 27, d.). Such appears to be a valvular 

 structure, and it is interesting that the lateral walls are thin, 

 the ventral arch thick, and the dorsal somewhat thin in the 

 median line, whilst the double stalk of the T is thick. The 

 double stalk of the T, indeed, widens, has the structure of 

 the gut, even to the vessels, on its walls, and gradually takes 

 the place of the wall in front, for it is apparently a valvular 

 invagination. If the serial sections can be relied on, it 

 would seem that in this region the sinus breaks up into 

 longitudinal vessels, the ventral remaining as before. The 

 gut is of various shades of brown or reddish brown, the 

 glands of its walls usually being brown by transmitted light. 

 Toward the tail (PI. VI. fig. 34) the chief feature is the 

 diminution of the canal and the larger size of the cells of the 

 cylindrical epithelium, which is richly ciliated, lining it. 

 The wall of the gut is sometimes folded, but no distinct 



