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 cosca. These seem to be merely blind evaginations, and 
gradually assume a lanceolate form, as we find in young cod from } to 14 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 (/wy) 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 (@) 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. stomodzeum 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 almond-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 Dourn 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 
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 hang down like two mem- 
branous flaps, diminish, and become denser on account of the development in their tissue 

assumes the shape found in the 
of maxillary bars, the chitinous character and form of which are elsewhere described. 
* Parker describes a true stomodeum in the salmon, but probably his account of the ingrowth of epiblast to 
form the mucous membrane of the mouth and fauces requires confirmation. 
+ Dourn, on the contrary, describes the centre of the oral slit as still closed when the lateral portions have broken 
through. 
