443 



presence of shed epithelial cells in the digestive but did not enter 

 fully into the question of their origin. 



It seemed desirable to re-examine the subject, and especially to 

 subject the digestive tract of the salmon under various conditions to 

 minute histological investigation, which has never yet been done. 



The Stomach of Salmon entering the River. 



The organ is surrounded by a serous coat, while beneath this are 

 two layers of non-striped muscle, the external thin and longitudinal, 

 the internal circular and five or six times as thick as the outer one. 

 Between the two layers run blood vessels, lymphatics, and a nerve 

 plexus, with an unusually large number of nerve cells, often grouped 

 together into comparatively large ganglia. Beneath the muscular layers 

 lies the submucosa, with many large blood vessels. The muscularis 

 mucosae consists of two layers, an external longitudinal and more 

 delicate, and an internal circular rather thicker layer. In the 

 mucosa the mass of connective tissue underlying the glands is very 

 considerable, being often nearly as thick as the glandular layer, and 

 is itself divided into two layers by the remarkable structure de- 

 scribed by Oppel in the stomach of the trout, the "membrana com- 

 pacta" or "stratum compactum". This layer, in whatever plane the 

 stomach is cut, is always found as a compact hyaline band lying rather 

 nearer the muscularis mucosae than it does to the fundi of the glands. 

 It contains no nuclei, and no structure can be made out in it by ordi- 

 nary methods. Nuclei lie upon it, however, and the fibres of the con- 

 nective tissue on either side are directly continuous with it (Fig. 4), 

 and behave to all reagents in the same way as it does. It is, there- 

 fore, certainly of connective tissue origin, and is as certainly not elastic 

 tissue as staining with orcein shows. The fibrous tissue outside this 

 layer is more delicate than that inside it, and the inner layer contains 

 more blood vessels, especially large venous spaces, than the outer 

 one. A special feature of both layers is the large number of large 

 eosinophile leucocytes to be found in the meshes of the connective 

 tissue; in fact, all the many leucocytes present here seem to be of 

 this variety (Fig. 4). 



In the epithelial lining of the mucous membrane the cells are of 

 three types: — 



1) The superficial epithelium and that forming the ducts of 

 the glands. 



2) The intermediate epithelium of the glands. 



3) The zymin-forming epithelium of the glands. 



31* 



