774 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
Anus.—The anus in the forms here described is not a proctodzeum, as it is not 
produced by the ingrowth of the external epiblast, but is at first a lateral opening (see 
Pl. VIL. figs. 12-15), which five or six days after hatching is formed by the protrusion 
of the anal section of the alimentary canal. In Molva vulgaris, early on the second day 
after emerging, the anal tract seems still to end blindly, being continued backward 
nearly in a straight line, or in some cases sending down a terminal process at right angles 
to the main axis of the canal. This terminal prolongation is carried down to the middle 
of the marginal fin, and generally on the second or third day is found to break through 
in a manner not unlike the oral opening. The rectum is thus a eapacious thick-walled 
tube, sending out a narrow anal continuation consisting of a fine tube lined by a single 
layer of cubical epithelium, and it passes through the thick tenacious plasma contained in 
the space behind the urinary vesicle (Pl. VII. figs. 12, 13). This space is enclosed between 
the two epiblastic lamellze of the caudal membrane, and the anal tube curves round and 
opens laterally on the surface of the latter, some distance from the ventral margin. 
Later the membrane below the aperture becomes absorbed, the rectum assumes thicker 
walls (hg, Pl. VIL. figs. 8, 9), and the usual muscular rectal portion of the alimentary 
canal is formed during the second week after emerging. The anus then opens in the 
ventral middle line, as in the adult fish. 
Liver.—Soon after the otocysts are formed the ventral wall of the mesenteron in its 
fore part shows an enlargement— an ovoid dilatation just before and below the early 
pectorals,” according to LerEBouLtLer (No. 93, p. 584), and his description holds to a 
large degree for pelagic Teleosteans. Certainly the liver is a distinct outgrowth from 
the ventral wall of the mesenteron. Horrman has expressed the view that the liver 
originates from the yolk-periblast, and that the hepatic diverticulum is really a prolifera- 
tion of ‘“ parablast entoderm” (No. 69a). Such sections as fig. 2, Pl. VIL, do not 
support this view, for the periblast (per) is a distinct, granular layer beneath, and 
separated by a delicate stratum of hypoblast (Ay) from the cells which build up the liver. 
The liver, in fact, is largely a solid proliferation of the ventral wall of the mesenteron, and 
is periblastic, or formed of “ parablast entoderm ” only in the degree that the ventral wall 
of this region is periblastic, and this we have seen at this point to be at a minimum. 
Into the early liver (/r, Pl. VII. fig. 5) a delicate canal (de) passes, a direct prolongation 
of the enteric lumen, doubtless the ductus choledochus. LrreBouLLer noticed this 
especially when the mesenteron dilated and contracted as it does in later embryonic 
stages (No. 93, p. 593). In Perca, on the sixth day, the same observer describes 
numerous ramifying fissures or prolongations from this delicate canal; and the gall- 
bladder he regards also as a tubular outgrowth of the intestine. The hepatic pro- 
liferation becomes bifid, a dorsal and a sinistral ventral lobe being distinguishable. The 
liver also becomes divided into small lobuli (/7, Pl. VIL. figs. 1-3), in the midst of which 
the spacious gall-bladder (gb) appears as a clear vesicle, limited by an epithelial wall 
of a single layer of cells. 
Swim-Bladder.—From the dorsal wall of the mesenteron (mg) the swim-bladder (sb) 
