274 



Pit d III. — Eleventh Annual Report 



VII. — ON THE DEVELOPMENT OF THE PLAICE (Plcuronrrtcs 

 p/atessa). By J. H. Fullarton, M.A., D.Se., F.R.S.E. (Plates 

 XIIL-XVI.) 



Part II. 



In the Ninth Annual Report,* I gave a general account of the develop- 

 ment of the plaice, as exhibited by mounted preparations of whole 

 embryos, and now propose to give some of the results of my investigation! 

 into the origin of the liver, heart, and renal organs, and the changes that 

 take place in these before the absorption of the whole of the yelk. In my 

 preliminary communication I pointed out that the larvae hatched in sixteen 

 and a half days after the fertilization of the ova. This period, as well as 

 the prolonged time taken between the extrusion of the embryo and the 

 absorption of the yelk, permit of a greater number of stages being obtained 

 than would otherwise be the case if the temperature of the sea-water were 

 higher. 



The first indication of the liver appears in the embryo of the ninth day 

 after fertilization, immediately behind the auditory vesicle. Lereboullet^: 

 in dealing with the development of the trout, perch, and pike, says : — 

 ' On remarque, contre la paroi exterieure de cette ampoule gastrique, une 

 accumulation de cellules, premier indice du foie. } In the plaice no such 

 ampoule is discernible at this stage, as the digestive tube maintains a 

 fairly uniform calibre for some distance from the origin of the liver, both 

 anteriorly and posteriorly. The cells of the ventral surface of the intestine 

 proliferate, as is shown (fig. 1, Ir.) from the increase of the nuclei, which 

 are three, and in some places four, rows deep on the under portion, whereas 

 the dorsal portion is only a single layer of cells thick. Coincident with 

 this multiplication of nuclei, the size and shape of the ventral cells — which 

 at first were regularly columnar like those of the upper surface — are con- 

 siderably altered, though the prevailing columnar shape obtains for some 

 time. The thickened ventral portion of the intestine forms the ventral wall 

 of the intestinal tube and the liver, and the transverse horizontal diameter 

 of the lumen of the gut becomes greater than the transverse vertical 

 diameter. This is the only change that takes place in the gut at this 

 stage, or till fully a day afterwards. The liver is separated from the yelk 

 by a very thin layer of hypoblast (hy.). Vogt§ describes the liver of the 

 salmon at first as ' un amas arrondi de cellules, adherant, d'wie part a 

 V elargissement de Uintestin, et, d' autre part, au vitellus.' No widening or 

 elargissement is noted in the plaice, and the liver certainly is not adherent 

 to the vitellus, for a thin but distinct layer of cells intervenes between it 

 and the latter. Probably the ampoule of Lereboullet, and the elargisse- 

 ment of Vogt, refer to a later stage, for it is very difficult, without a study 

 of sections, to determine the earliest appearance of the liver, or of the cells 

 that go to form the liver. 



The intestine widens in embryos about a day further advanced, but the 

 widening is morphologically different from that described by Lereboullet,§ 

 who says in reference to the intestine : — 1 le tube se renjle en une am/poide 

 qui constitue le rudiment de Vestomac' In fig. 2, the first widening that 



* Ninth Annual Report of the Fishery Board for Scotland, Part hi., pp. 311, ct scq. 



t I have to thank Mr F. G. Binuie for the faithful drawings of my sections on 

 the accompanying plates. 



X ' Rechercbes d'Embryologie comparee sur de developpement du Brochet, &c.,' 

 Mem. Sav. Etrang. Acad, des Sc., torn. xvii. 



§ Embryologie des Salmoncs, in Histoire Naturelle des Poissons d'Eau douce de 

 1' Europe centrale, par L. Agassiz. Neuchatel, 1842. 



