PYLORIC CAECA 



275 



Siluridae, Esocidae, Cyprinodontidae, Labridae, Plectognathi, and 

 Lophobranchii. The "Sand-eel" (Ammodytes) has but a single 

 caecum ; the Turbot (Rhombus maximus) two, and other Pleuro- 

 nectidae three to five; and the Perch (Perm), three (Fig. 160, 

 py.c). 



In other Teleosts, on the contrary, these structures are much 

 more numerous. In Ldbrus labrax there are about 60, in the 

 Whiting (Gadus merlangus) 120, while in the Mackerel (/v//< //,>/ 

 scombrus) there are no fewer than 191. If few in number the 

 caeca open separately into the intestine, but when numerous, 

 more or fewer of them may unite to form a smaller number of 

 efferent ducts, as in the AVhiting, where four such ducts are 

 formed. In some instances, as in the Tunny (Thunmis), the 

 union of the caeca by connective tissue leads to the formation of 

 a compact mass. As regards their arrangement, the caeca may 

 either be disposed in a whorl round the intestine, as in the 

 AVhiting, or in a linear series, as in the 

 Salmon (Salmo) and in some of the 

 Clupeidae. 



The mucous membrane lining the 

 anterior pyloric caeca is often developed 

 into a network of ridges, limiting crypt- 

 like or tubular depressions ; and not in- 

 frequently the epithelium is ciliated. 



The precise function of these organs, 

 whether digestive or absorptive, is still 

 uncertain. 1 That they may be digestive 

 is suggested by the presence of certain 

 amylolytic and proteolytic enzymes, but 

 this obvious conclusion is to some extent 

 vitiated by the close proximity of these 

 organs to the stomach, and more especially 

 to the intestinal orifice of the pancreatic 

 duct. It is by no means improbable, 

 however, that the caeca are both digestive 

 and absorptive organs. An attempt has 

 been made to show that the pyloric 

 caeca and the spiral valve vary inversely 

 as regards the extent of their development in different groups of 



1 For references, see Macallum, Journ. Anat. and Phys. xx. p. 624 ct scq. 



-an. 



FIG. 160. The alimentary 

 canal of a Perch (Perca). 

 (in. Anus ; in. intestine : 

 oes, oesophagus ; py, 

 pylorus ; py.c, pyloric 

 caeca ; st, stomach. (After 

 Wk-dersheiiu. ) 



