310 PROFESSOR FRANK J. COLE 



the better developed, but I agree with Schreiner that the dorsal folds are usually the 

 stronger. Ma as holds that the folds of the abdominal gut are not to be horaologised 

 either anatomically or physiologically with those of the pharyngeal gut, basing the 

 distinction on the behaviour of the muscularis mucosae, which I do not find anywhere in 

 the gut, and on the assumption that the stratum compactum is confined to the abdominal 

 gut, with which I do not agree. His assertion, therefore, that in the one case the folds 

 of the mucosa do not affect the underlying tissues, but do in the other, is one which may 

 well be questioned. In 8-9 cm. Hags he finds the abdominal folds only faintly defined. 



The mucous epithelium of the abdominal gut is entirely different from that of 

 the pharyngeal gut. It is single-layered, and there are no traces of the glassy and 

 granular mucous cells. There are, however, numerous highly granular unicellular 

 gland cells, which are highly eosinophilous. The free border of the epithelium is 

 striated ; and nearer the lumen end of the cells, i.e. outside the nuclear zone, there are 

 many diffuse mitoses. The mucosa is pitted, and is very easily detached from the 

 submucosa owing to the extensive lymph sinus between the two layers. Both Maas 

 and Schreiner describe a slender basement membrane which I have not found. It is 

 possible they may be referring to a membrane between the mucosa and the stratum 

 compactum, and which appears to me to belong to the latter layer. 



There is no muscularis mucosae, but in its place Maas describes what he calls the 

 peculiar and characteristic stratum compactum, which is highly vascular, and dispatches 

 supporting processes into the adjacent lymphoid tissue. Maas has devoted consider- 

 able attention to this tissue, without, however, noticing that it is strictly comparable to 

 the submucosa of the pharyngeal gut. His digestion experiments establish that it is 

 not one of the elastic connective tissues, and he holds that the connective-tissue frame- 

 work of the abdominal gut is more specialised than that of the pharyngeal gut, since 

 the embryonic formative cells have more and more receded in favour of the cell product. 

 The obvious and important blood sinus which is seen in the stratum compactum 

 immediately under the mucosa is usually flushed with blood, and has a definite lining 

 with longish flattened nuclei. Maas w^as unable to find this lining. 



External to the stratum compactum is the lymphoid portion of the submucosa, and 

 then follow the weak circular unstriated musculature (no longitudinal musculature) and 

 the serosa with its attached connective tissue. 



The lymphoid submucosa is very vascular, and is continued into the folds of the 

 mucosa. Its characteristic feature is the presence of packets of lymph cells associated 

 with the factors of the portal vein, but not with the arteries. Such lymphoid tissue 

 in the wall of the gut occurs in a very few forms {e.g., Protopterus) , and Maas regards 

 it as a diffuse spleen, holding that the compact spleen of the higher forms has been 

 produced first by the concentration of such a tissue, and then by its emergence from, 

 the wall of the gut. Maas, who overlooked the essentially adipose nature of the 

 lymphoid zone, observed by Schreiner shortly before, states that the lymphoid heaps 

 only occur in the more peripheral regions, and then specially round the smaller veins. 



