of the Fishery Board for Scotland. 



41 



PART II. 



HISTOLOGICAL INVESTIGATIONS ON THE DIGESTIVE 

 OEGANS OF FISHES. 



The literature regarding the structure of the intestinal tract in fishes is 

 given in Owen's Comparative Anatomy of the Vertebrata. The most 

 recent investigation upon this subject is that by Edinger — Ueber die 

 Sehleimhaut des Fischdarmes nebst Bemerkungen zur phylogenese der 

 Driisen des Darmrohres* Edinger investigated the structure of the 

 mucous membrane of a large number of fishes. A list of the chief 

 publications on this subject prior to Edinger's investigations are given afe 

 the commencement of his paper. 



Methods of Investigation. 



The tissue to be investigated was hardened by the usual methods. 

 After making a trial of several methods, I think on the whole the best 

 results were obtained by distending and hardening the intestinal tract in 

 a mixture of Miiller's fluid and spirit (3:1). Small pieces were also 

 hardened in osmic acid (J-l per cent.), and for gland texture absolute 

 alcohol was used. In fact, all three methods were employed. For the 

 isolation of the epithelium I used Ranvier's dilute alcohol, osmic acid 

 (j-L- per cent.), and what I found very useful for the cells of the cardiac 

 sac, a solution (3-5 per cent.) of ammonium or potassium sulphocyanide. 

 The mucous membrane, when macerated for twenty-four hours in this 

 solution, is readily broken up. The dissociated epithelial cells may then 

 be acted upon by osmic acid (1 per cent.), which * fixes 7 them, so that 

 they may be preserved for a length of time. 



THE HERRING. 

 The (Esophagus. 



As a general rule in fishes, the mucous membrane of the oesophagus is 

 provided with a series of permanent longitudinal folds. In the herring 

 these folds are not so obvious as in some other fishes, such as the 

 haddock. On examining the mucous membrane of the oesophagus from 

 above with a low power, and by means of reflected light, one sees a 

 number of sinuous folds with smaller secondary folds. These sinuous 

 folds leave between them longitudinal depressions. On examining the 

 continuation of the oesophagus into the upper part of the cardiac sac, the 



* Archiv. f. mik. Anat., vol. xiii. p. 651. 



