In some Teleosts (Siluroidea, Labroidea, Cyprinodontia, Plectognathi and Leptobranchiates) the appendices are entirely wanting. If there are not more than 8-10 appendices they usually surround the gut and empty into the same in a circle. In other cases they are arranged in a single line, or in a double row, opposite to each other (Fig. 213). Each appendix may open into the intestine independently, this especially where the number is limited and the individual pouches large (cf. Figs. 206-210), or several may unite to form a common duct. [Illustration: FIG. 213.--_Melanogrammus aeglifinus_, haddock. Stomach, mid-gut, and pyloric caeca; spleen. (Columbia University Museum, No. 1598.)] Fig. 211, _B_, shows the appendices in _Gadus callarias_, the cod, freed by dissection from the investing connective and vascular tissue. It will be noticed that a considerable number of the tubes unite to form ducts of larger caliber which open into the intestine, as seen in the section shown in Fig. 214. [Illustration: FIG. 214.--Stomach and mid-gut of _Gadus callarias_, codfish, in section, showing intestinal openings of pyloric caeca. (Columbia University Museum, No. 1830.)] The pyloric appendices apparently have the same _significance_ as the spiral intestinal fold of the Selachians, Cyclostomes and Dipnoeans, _i. e._, the production of an increase in the area of the digestive and absorbing surfaces of the intestinal mucous membrane. Hence, as stated, the appendices and the spiral fold are found to vary in inverse ratio to each other. Thus, for example, _Polypterus_ (Fig. 205) still has a fairly well developed spiral fold and only a single pyloric appendix, while _Lepidosteus_, with but slightly developed spiral fold, has numerous appendices. It was formerly held that the pyloric caeca and the pancreas were mutually incompatible structures, and that where one is found the other will be wanting. Hence the appendices were regarded as homologous with the pancreas of the higher forms. Recent observations have shown that this view is not strictly and entirely correct, while at the same time it merits consideration in several respects. It is true that the pancreas in certain teleosts is now known to be present although concealed from observation in the liver or scattered in the form of small lobules between the layers of the mesentery (cf. p. 117), and that in a number of fish, such as _Salmo salar_, _Clupea harengus_, _Accipenser sturio_, both the appendices and the pancreas are encountered. Consequently these structures are not identical or even completely homologous, since they occur side by side in the same form. On the other hand Krukenberg has demonstrated that the appendices pyloricae may function physiologically as a pancreas by yielding a secretion which corresponds to the pancreatic juice in its digestive action. In the majority of forms, however, they apparently merely increase the intestinal absorbing surface, secreting only mucus.