. The Cambridge natural history. Zoology. PYLORIC CAECA 275 Siluridae, Esocidae, Cyprinodontidae, Labridae, Plectognathi, and Lophobranchii. The " Sand-eel" {Ammodytes) has but a single caecum; the Turbot {Ehotnhus maximus) two, and other Pleiiro- nectidae three to five; and the Perch (Perca), three (Fig. 160, ). In other Teleosts, on the contrary, these structures are much more numerous. In Lcibrus lahrax there are about GO, in the Whiting {Gadus merlangus) 120, while in the Mackerel {Seomher scomlrus) there are no fewer than 191. If few in number the caeca open separately into
. The Cambridge natural history. Zoology. PYLORIC CAECA 275 Siluridae, Esocidae, Cyprinodontidae, Labridae, Plectognathi, and Lophobranchii. The " Sand-eel" {Ammodytes) has but a single caecum; the Turbot {Ehotnhus maximus) two, and other Pleiiro- nectidae three to five; and the Perch (Perca), three (Fig. 160, ). In other Teleosts, on the contrary, these structures are much more numerous. In Lcibrus lahrax there are about GO, in the Whiting {Gadus merlangus) 120, while in the Mackerel {Seomher scomlrus) 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 eiferent ducts, as in the "\^'hiting, where four such ducts are formed. In some instances, as in the Tunny (Thunnus), 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 Whiting, 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 ' 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 ' For references, see Maoallum, Journ. Anat. and Phijs. xx. p. 621 et Fig
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
