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Part III. — Eleventh Annual Report 



angle of about 90 degrees, the walls, which are of distinctly columnar 

 cells, diverge from one another, forming the lumen of the gall-bladder. 

 In fig. 6 the part of the ductus choledochus, which becomes the cystic 

 duct, has a single-celled layer of regular columnar cells, while the walls of 

 the bladder proper are composed of cells which have not yet assumed the 

 columnar form, though they exhibit nuclei with nucleoli at irregular dis- 

 tances. So the 1 vesicule biliaire 1 may be considered as ' se produire par 

 exsertion de Vintestin.' While the duct as a diverticulum of the intestine 

 has been lengthening, papillae have been developing from the walls of the 

 intestine into its lumen, and the intestine itself is being coated with 

 muscular fibres. Not only the gall-bladder but the ducts may be regarded, 

 as Lereboullet describes the former, ' un appendice intestinal? 



I have seen nothing corresponding to the description and fig. (No. 141) 

 which Vogt gives. In all my sections there is only a single diverticulum 

 from the intestine entering the liver, thus differing from Balfour's * de- 

 scription and fig. 421 of the development of the liver in Scyllium, where, 

 though the diverticulum may be at first single, it may afterwards grow 

 out into two lobes, and also from Gotte's figures of Bombinator and the 

 Chick, as given in Balfour's Embryology, figs. 420 and 422. In Bom- 

 binator the figure makes the liver a pouch, but in the plaice the pouching 

 is only secondary to the pronounced thickening of the ventral wall of the 

 intestine. In fig. 15 the cells of the diverticulum, which in fig. 5 gradually 

 melted into the cells of the liver, have now become quite distinct from the 

 latter, and the diverticulum ends caecally. The wall at the caecal end appears 

 greatly thickened, but this is accounted for by the section being slightly 

 oblique at this point. Figs. 22 and 23 show the duct in transverse section 

 in an embryo a few hours older, and fig. 14 shows very distinctly the 

 opening of the ductus choledochus into the intestine, and also a transverse 

 section through the thick wall of the duct (g.b.) more vertically. No single 

 section shows the entire duct from the intestine to the gall-bladder, but 

 it is easily traced in a series of sections, throughout its whole length. 

 Figs. 6 and 7 show the duct, in the first, proceeding from the gall-bladder, 

 and, in the second, arising from the left side of the intestine, and curving 

 round it for half its circumference, so that, though the sections are taken 

 from two embryos of nearly equal ages, they represent practically the 

 whole course of the duct. Five days after the first indication of the liver, 

 the organ shows two lobes, and in figs. 22 and 23, drawn from sections of 

 embryos of this age, the formation of hepatic lobules takes place in the 

 liver, which has just become bi-lobed. 



The results put shortly are these : — The liver is formed by the prolifera- 

 tion of cells from the ventral wall of the gut ; the ductus choledochus is a 

 diverticulum from the intestinal tube, it is always single, and a dilatation 

 of this tube forms the gall-bladder. 



While the agreement between embryologists, who have treated of the 

 Teleostean liver, is nearly absolute, a difference of view is encountered 

 when we come to consider the origin of the heart and the structure from 

 which, especially, the endocardium has been formed. 



The heart arises underneath the still solid oesophagus, and in close 

 proximity to it. It is situated in the region below the mid and hind 

 brain, and occupies a position in the angle between the anterior border of 

 the yelk-sac and the head of the embryo. The heart, as a tubular struc- 

 ture, is primarily the endocardium alone, the development of myocardium 

 being later, as will be seen from a consideration of sections of about the 

 eighth day. The accounts given by different authors, who have treated of 

 the development of trie vascular system, show a diversity of opinion. It 

 is quite impossible to trace the origin of the heart, either in the living 

 * Comparative Embryology, vol. ii., London, 1881. 



