GIZZARD IN FISHES m 



distinct pyloric division of the stomach, the 

 material for a hard muscular gizzard exists. It 

 is obvious that the constitution of the alimen- 

 tary canal depends upon the nature of the food. 

 Comparative anatomy and physiology teach us 

 that the digestive tract reacts to different condi- 

 tions of nutrition; but not many such unequivocal 

 demonstrations of the independent acquisition, 

 within the limits of an order, of a compact 

 specialised structure as that described above, 

 can be pointed to. 



Regarding the families of the Mugilidse and 

 Clupeidse in their entirety, we have now con- 

 sidered two characters with respect to which 

 they converge, namely, the adipose eyelids (above, 

 p. 94) and the pyloric gizzard. In both of these 

 cases, as well as in that of the pectoral fins of 

 the flying fishes, we have anatomically identical 

 structures arising independently from a common 

 origin. Facts of this nature apparently take the 

 ground away from any intelligible conception of 

 homology — but only apparently. The relations 

 can be illustrated graphically, as shown in the 

 diagram (Fig. 11). 



The gizzard of the mullet was known to John 

 Hunter, 1 who tells us that of all the fish seen 



1 John Hunter, "Observations on the Gillaroo Trout, commonly 

 called in Ireland the Gizzard Trout," Phil. Trans. , 1774; reprinted 

 in his "Animal Oeconomy," which was republished in vol. iv. of 

 Hunter's Works, edited by James F. Palmer, 1835-1837. Here 

 also is to be found Hunter's paper, " On a Secretion in the Crop 

 of Breeding Pigeons, for the Nourishment of their Young." 



