1 68 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



development of longitudinal and transverse folds : the 

 most remarkable of these ingrowths is one that we 

 cannot refrain from associating with the typhlosole of 

 the earthworm and of the fresh-water mussel ; when 

 best developed, as in the elasmobranchs, this fold 



Fig. 76. Stomach of Desmodus, in the form of a long caeca! process. 



forms a spiral valve. In a more rudimentary con- 

 dition it is presented as an incomplete spire in the 

 lampreys, as consisting of thin whorls in the chi- 

 msera, or of varying degrees of complication in various 

 ganoids, and as sometimes forming a closely appressed 

 series of folds in the skate. Among the Teleostei it 

 is very rarely developed, though a projection of this 

 kind is certainly to be seen in some specimens of 

 Chirocentrus, and has been expressly said to be found 

 in Butiriiius (Stannius). In the Teleostei there appear 

 tubular outgrowths of the upper end of the small 

 intestine, which may be supposed to take the place of 

 the absent spiral valve ; these pyloric appendages, 



