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shorter in fishes than in most of the higher vertebrata. But 

 the length of the intestinal tract differs in various classes, 

 while its lining membrane is by no means of the same de- 

 scription in all. In the salmon or herring we find the 

 length of the intestines shorter than that of the body, 

 but in the former the intestinal lining membrane is raised 

 into transverse folds, thus increasing the extent of their 

 secreting surface, which is also further augmented by the 

 presence of numerous csecal appendages, which I shall 

 have presently to allude to. In the herring, again, the 

 caecal appendages are numerous. In other forms we find 

 the intestines themselves convoluted, thus increasing their 

 length, and this is well seen among the carps, especi- 

 ally in such as are herbivorous. In the salmon the folds 

 of the internal lining of the intestines increase in size, de- 

 crease in number, and become less oblique as they approach 

 the rectum, and, as observed by Owen, the commencement 

 of the large intestine is marked by a large transverse fold 

 or circular valve, which is succeeded by several others less 

 produced, and resembling the Valvulce conniventes in the 

 human jejunum. This large intestine may be straight, att 

 seen in the sturgeon or chimaera, &c., where the transverse 

 folds (as observed existing in the salmon) become con- 

 tinuous, and there is formed an uninterrupted spiral valve, 

 also present in the sharks, the rays, and their allies, but 

 which may be modified into transverse coils. 



It is thus that in fishes economy of space is effected by 

 an increase of the secreting and absorbing surface of the 

 vasculo-mucous membrane lining the intestinal tract, 

 whether such be merely raised into puckers, or these 

 puckers be continued into transverse folds, or even form- 

 ing a circular uninterrupted spiral valve or coil to the large 

 intestine. 



