924 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



In the young Pleuronectid, -^ inch long, the liver is of considerable size, and fills up 

 the main part of the large peritoneal cavity in front. This chamber is very capacious, 

 and causes the abdomen to hang like a swollen sac on the ventral side of the young fish. 

 Its walls are thin, a delicate sheet of muscle merely intervening between the integument 

 and the internal peritoneal lining. Posteriorly the spacious intestine fills up the cavity. 

 Anteriorly the narrow oesophagus passes above the liver; but in many forms it descends 

 into the hepatic mass — so deeply in the salmon and in the wrasse -^ inch long as to be 

 almost enveloped by the liver, as we see in a less degree in the Gadoid when -f inch in 

 length. 



The gall-bladder forms a large rounded diverticulum in the midst of the liver on the 

 right side. The outer layer is fibrous and probably muscular, while the inner consists of 

 flattened, epithelial cells. At this stage two apertures are visible, one leading from the 

 anterior division of the liver by a somewhat convoluted duct, the other entering the 

 bladder towards its posterior border on the same side, i.e., the left. 



Spleen. — In the gurnard, \ inch long, and skulpin, ^ inch long, a rounded 

 body occurs behind the liver. It is sheathed in a delicate cellular wall, and is formed 

 of cells which stain deeply, grouped together in clumps, and forming a fairly solid 

 organ. In Cottus scorpius, f- inch long, an organ of similar histological structure 

 passes along the posterior dorsal surface of the liver. No limiting membrane separates 

 it from the liver, but its cells stain more deeply than those of the hepatic mass. Its 

 form is flattened and lobular, with blood-corpuscles filling up its interstices, and it is 

 apparently the spleen. 



Branchial System. — On the first day the branchiae of the salmon have simple rows of 

 papillae, each with a loop formed by a blood-vessel. On the second or third day, probably 

 somewhat earlier, the operculum is noticed to flap actively, and a single series of blood- 

 corpuscles rush up one side and down the other side of the branchial fimbriae. Small- 

 celled cartilage is present in the branchiae on the eighth day, and respiration is active, 

 while on the fourteenth day, the embryo respires 106 to 108 times per minute. On the 

 nineteenth day (sixth to seventh week after fertilisation) the branchial fimbriae are pro- 

 portionately large and blunt. 



In the wolf-fish each branchial arch, on the 16th January, presents externally the 

 cuticular investment, then a dense cellular layer (hypoderm) of connective and glandular 

 tissue, this being greatly thickened on the margin, which afterwards becomes laminated. 

 The cartilages of the arch have in transverse section a thick marginal structureless ring 

 and a cellular centre. The papillose processes in Anarrhichas, on the thickened edge, 

 increase in size in February, but they do not show much further differentiation during 

 this month. In March the branchial papillae are simple, and their vascularity is evident 

 towards the end of the month, a large loop occurring in each. In April the elongated 

 process becomes pinnate, a feature still more evident in May, so that each is feather-like, 

 after the plan of those figured in the very young flounder (PI. XV. fig. 8). Little further 

 change ensued in those examined in June. 



