IX PYLORIC CAECA 275 
Siluridae, Esocidae, Cyprinodontidae, Labridae, Plectognathi, and 
Lophobranchii. The “Sand-eel” (Ammodytes) has but a single 
eaecum ; the Turbot (Rhombus maximus) two, and other Pleuro- 
nectidae three to five; and the Perch (Perea), three (Fig. 160, 
pyc). 
In other Teleosts, on the contrary, these structures are much 
more numerous. In Labrus labrax there are about 60, in the 
Whiting (Gadus merlangus) 120, while in the Mackerel (Scomber 
scombrus) there are no fewer than 191. If few in number the 
eaeca 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 Whiting, where four such ducts are 
formed. In some instances, as in the Tunny (Zhunnus), the 
unicn 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 
uncertain.’ 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, arene ay en 
however, that the caeca are both digestive an, Anus; in, intestine ; 
and absorptive organs. An attempt has ee a Saat 
been made to show that the pyloric — caeca; st, stomach. (After 
eaeca and the spiral valve vary inversely ee one 
as regards the extent of their development in different groups of 
t--an, 
1 For references, see Macallum, Journ. Anat. and Phys, xx. p. 624 et scq. 
