52 ME. W. S. EOWXTEEE ON THE 



Tbue Characinidve: Hekbivoka. 



(Tropical America.) 



49. Prochilodus lineatus. 



50. Curimatus dobula. 



(Tropical Al'rica.) 



42. Distichodus niloticus. 



43. „ Antonii. 



44. Nannocharax mJoticus. 



45. Xenucharax spUurus. 



46. Citharinus Geoffroyi. 



47. ,, latus. 



48. „ congicus. 

 48 «. „ macrole/iis. 

 48 h. Citharidium Aiisoryii. 



The Alimentary Canal and its Appendages. 



The Stomach. 



In Characinids the short gullet passes often insensibly into the stomach, but in some 

 cases the transition is marked hj a sudden change of calibre or of wall-thickness. This 

 latter condition I have observed more particularly in Distichodus, Sei^rasalmo, Lebiasina, 

 Alestes nurse, and Leporinus. 



The stomach has the form of a more or less expanded sac, of variable size, bent shar2:)ly 

 on itself at the pyloric region. This flexure is usually A^eatrally directed (PI. 3. fig. 1). 

 But I have found numerous exceptions. In Sarcodaces the flexure was dorsal in every 

 one of the nine specimens exaiTiined (fig. 2). In Macrodon and Erythrinus also the 

 flexure was dorsal or Isevo-dorsal (fig. 3). In all the sixty-three specimens of Ichthyo- 

 horiis, which happened to be examined for a special purpose, the flexure w^as directed to 

 the left side. In Uijdroeyon Forskalii (several sjiecimens) the stomach was flexed 

 towards the right side. In Nannocharax, E^tgnathichthys, and Phago the flexure was 

 dorsal. The regularity with which these conditions Avere found was somewhat striking, 

 although one can scarcely attribute any great significance to them. 



The anterior or cardiac chamber of the stomach is usually much more capacious than 

 the ascending or pyloric liml). It is, moreover, at least in some forms, highly distensible; 

 the lining membrane, wdiich is often deeply rugose when the stomach is empty and 

 contracted, becoming quite smooth when the organ is distended with food. At the 

 same time tlie stomach-wall, which may in the contracted state appear quite thick and 

 fleshy, thins out and becomes so transparent that the contents become visible even in 

 detail. Thus in one instance {Sarcodaces), where an entire Anabas was found in the 

 stomach, the species of the ingested fish could be easily identified wdthout opening the 

 organ. The distension takes place longitudinally as well as transversely. The organ 

 may indeed stretch to the full limit of the body-cavity, although in its contracted state 

 not exceeding half that length. In the instance above referred to the length of the 

 distended stomach, drawn tightly over the contained fish, was 11 cms., the Sarcodaces 

 itself being only 25 cms. long. It is obvious, in view of the narrow and acutely 

 reflected pyloric limb, that the stomach mu.st possess great digestive activity. Fig. 2 



