252 



Prof. M'lntosh's Notes from the 



apparently uniform, and contain mud rich in organic 

 remains. 



The former or stomachal region enters the following or 

 intestinal region by an aperture which is thrust backward as 

 a cone. Moreover, the walls of the organ undergo a struc- 

 tural differentiation, for a short distance before reaching the 

 aperture (text-fig.) they become finely reticulated and dotted 

 as if formed of muscular or erectile tissue {ec), whilst the 

 lining of the tube consists of the same mucous membrane 

 as in front. Further, the adjoining circular fold of the 

 diaphragm {spt. 3) is provided with a similar, though 

 thinner, layer of the same tissue (ec), which likewise 



Longitudinal section of the alimentary apparatus at the third septuu), 

 spt. 3, showing traces of the special muscular layer, ec, enveloping 

 the posterior wall of the stomach and its sinuses, and continued 

 over the valvular region, veil. ; hp., hypoderm ; ccel.c, ccelomic 

 corpuscles ; ing., mucous glands. 



occurs in two of the folds of tlie organ in front of the 

 foregoing. This tissue is apparently muscular, and its 

 minute structure is interesting as showing the peculiar 

 muscle-cells with their granular contents and nuclei which 

 stud the free border of the muscle. Ziircher "^ has given a 

 good description and figures of the structure of this tissue. 

 It evidently controls not only the wall of the canal but the 

 blood-sinus on its outer surface, and thus may have con- 

 siderable effect on the main trunks proceeding forward 

 to the branchiae. The ccelomic corpuscles often form a 



* Op. cit. p. 203, and figs. 33 & 35. 



