DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 773 



stomach (st) follows, and beneath its thin walls the hepatic mass lies. A fourth portion 

 of the tract succeeds, viz., the pyloric section, the dense walls of which give origin to those 

 remarkable diverticula, the pyloric cceca. These seem to be merely blind evaginations, and 

 gradually assume a lanceolate form, as we find in young cod from \ to 1^ inch in length. 

 Ventrally a well-marked duct passes from the liver, viz., the ductus choledochus, with 

 several ramose biliary ducts. The intestinal walls are very dense, rapidly develop a glandu- 

 lar character, and have a narrow oval lumen (hg) with local enlargements, especially in the 

 mid portion of the gut. Posteriorly it narrows again until the rectal region is reached, 

 where a cincture or valve occurs, behind which its capacity once more enlarges (see 

 also hg, fig. 8 on the same plate) ; it then bends downward, and narrows to form the small 

 anal aperture (a) opening upon a muscular papilla. A similar condition of the intestine 

 and rectum is seen in the figure of P. platessa (PL XIV. fig. 5). The rugose walls often 

 exhibit vermicular movements, which are, however, very irregular, and involve and pro- 

 duce great contortions in the alimentary tract ; thus a peristaltic motion may pass from 

 the mesenteron to the rectum, narrowing its capacity as though by an embracing cincture. 

 Mouth. — A stomodseum or involution of epiblast to form the mouth is never really 

 formed in pelagic Teleosteans.* The oral cavity is capacious, and the branchial frame- 

 work supporting its floor and sides is fairly advanced when a fine transverse fissure is 

 seen passing across the under surface of the head below the eyes (m, PL IX. fig. 2). 

 This fissure enlarges and lengthens, forming an almoncT-shaped opening (m, PL IX. 

 fig. 3) across the subcephalic membrane. This is the mouth, and it is formed as a slit by 

 the lumen of the buccal chamber bursting through. Its edges are jagged, and strands of 

 cellular tissue often pass across from one lip to the other one or two days after the oral 

 opening appears (PL IX. fig. 3), showing that it is an actual severance of a complete 

 epiblastic membrane. There is no indication of the double origin, the coalescence of two 

 lateral clefts which Dohrn has described in Gobius, Belone, and Hippocampus (No. 52a) ; 

 but in the ling — the species illustrated in the figures just referred to, and in other forms 

 — this median transverse fissure suddenly appears, and in the course of two or three days 

 widens antero-posteriorly to form a large median tubular opening, t The lips do not 

 move, but the hyoid cartilages are flexible and mobile, and the floor of the mouth is thus 

 raised and depressed. The mandibular cartilages rapidly grow forward, and the oral 

 opening — at first ventral, transverse, and shark-like — assumes the shape found in the 

 adult Teleostean, the prolongation of the mandible not only bringing forward the aperture 

 of the mouth (PL XII. figs. 2, 6, 7), but proceeding so fast and to such a degree that the 

 floor actually extends beyond the snout, and the aperture now opens from above 

 (PL X. figs. 1, 2, 3, 5, 5a). The suborbital curtains, which haug down like two mem- 

 branous flaps, diminish, and become denser on account of the development in their tissue 

 of maxillary bars, the chitinous character and form of which are elsewhere described. 



* Parker describes a true stomodseuni in the salmon, but probably his account of the ingrowth of epiblast to 

 form the mucous membrane of the mouth and fauces requires confirmation. 



t Dohrn, on the contrary, describes the centre of the oral slit as still closed when the lateral portions have broken 

 through. 



