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Part III — Eleventh Annual Report 



day and a half before the first indication of the thickening of the ventral 

 wall of the gut, which gives rise to the liver. The diverticulum which 

 Miklucho-Maclay* observed in Selachians, arose from the dorsal side of the 

 gullet, while Van Baer, who first described the origin of the swim-bladder, 

 found that the outgrowth was placed slightly in front of the liver. In the 

 plaice the furrow observed is developed behind the fore-gut, though this 

 is not yet distinctly marked off from the mesenteron. It arises before 

 there is any trace of the formation of folds in the intestine, and disappears 

 within two days, before, in fact, the internal surface of the gut is increased 

 by the ingrowth of papillary prominences from the thickened walls. The 

 suggestion that this diverticulum may mark, what in other Teleosteans is 

 the swim-bladder, is put forward tentatively, and, the more posterior origin 

 notwithstanding, it may be the equivalent of the diverticulum that 

 Miklucho-Maclay found in the Selachians. 



EXPLANATION OF THE DRAWINGS ON PLATES XIII.-XVI. 



a, auricle. 

 ao, aorta. 

 br.c, branchial cleft. 

 b.v, blood-vessel. 

 d.c, ductus choledoclms. 

 d.f, dorsal fin. 



en, endothelium or endocardium. 

 ep, epidermis. 

 f.b, fore-brain. 



f. g, fore-gut. 

 9, gut. 



g. b, gall-bladder. 

 gl, glomerulus. 



h, heart (myocardium). 



h. b, hind-brain. 

 h.g, hind-gut. 



hi/, hypoblast. 



Ir, liver. 

 l.s.o, lateral sense organ. 

 m.b, mid-brain. 

 m.o, medulla oblongata. 

 my, myotome. 



nc, notochord. 



ne, neurochord. 

 p.c, pericardial chamber. 

 p.f, pectoral fin. 

 prn, pronephros. 

 s.d, segmental duct. 

 s.v, sinus venosus. 

 sw.bl, swim-bladder. 

 u.v, urinary vesicle. 



v, ventricle. 

 iv.c, wandering cells of mesoblast. 



Plate XIII. 



Fig. 1. Transverse section of an embryo 8 days 19^ hours old in the region of the 

 liver, x 250. 



Fig. 2. Median longitudinal vertical section of an embryo 10 days 7^ hours old 



through the mesenteron and liver, x 150. 

 Fig. 3. Longitudinal vertical section to one side of the middle line of the same 



embryo in the same region, x 150. 

 Fig. 4. Oblique longitudinal vertical section of an embryo 12 days 19^ hours old 



through the liver and its duct, x 150. 

 Fig. 5. Transverse section of an embryo of the same age in the region of the 



pectoral fin, x 150. 



Fig. 6. Transverse section of an embryo of 19 days — 2 days hatched — in region of 

 gall-bladder, x 200. 



Fig. 7. Transverse section of an embryo of 18 days — 1 day hatched — where duct 

 of liver, enters the intestine, x 200. 



* Of. Balfour. Loe. cit, p. 628. 



