of the Fishery Board for Scotland, 
311 
VI.— ON THE DEVELOPMENT OF THE PLAICE {Pleuronectes 
platessa). By J. H. Fullarton, M.A., D.Sc, F.R.S.E. (Plates 
VIL-IX.) ^ 
Preliminary Report. 
Ripe plaice were obtained by Mr Thomas Scott, F.L.S., when on board 
of the ' Southesk ' in January last, and fertilisation of the ova was effected 
on the afternoon of the twenty-seventh of that month. The fertilised 
eggs arrived at Dunbar Marine Laboratory on the following day, and the 
first of the larva3 hatched in sixteen and a lialf days, the remainder 
continuing to hatch during the following two days, when the last of the 
embryo plaice emerged through the egg-membranes. The average 
temperature of the sea- water of the vessels containing the developing eggs 
was 45° Fahr., and the daily range was within 3° more and 2° less than 
this figure. The slow rate at which development proceeded was entirely 
due to the low temperature of the sea-water during the last days of 
January and the month of February. After birth the complete absorption 
of the yolk-sac took other twelve days, so that the time taken from 
fertilisation till the absorption of all the yolk was altogether twenty-nine 
days, or, roughly speaking, one month. 
Preliminary to the treatment of the development of the species in 
detail, I w^ll here give a general account of the development, illustrated 
with drawings from fixed, stained, and mounted specimens of the whole 
embryo.* 
The changes immediately after fecundation were not observed by me, as 
the first living stages were twenty-six hours old before they reached me. 
Besides the corrugated surface of the egg-membrane, which has been 
noticed both by M'Intosh f and by Cunningham, J was very marked in 
all of the plaice ova, and the wrinkling makes observations on the earliest 
stages of the living egg more difficult to follow. On the formation of the 
blastoderm, as in other pelagic ova, the animal pole is ventral, the yolk 
mass being uppermost. Fig. 1 shows the blastoderm at the eight-celled 
stage, two of the cells showing each a nucleus. In other teleostean 
ova, flounder, herring, sand-eel, &c., I noticed the formation of the 
first furrow when it began as a slight depression of the blastodisc, 
which gradually became deeper, till the germ was divided into two large 
cells. The blastoderm of eight blastomeres shows one longitudinal and 
three transverse furrows, one pair of cells being slightly in a different 
plane from the other three. At this stage there is undoubtedly no 
horizontal furrow, all the furrows being perpendicular to the basal plane 
of the germ, a result in accordance with the statements of other observers 
on teleostean segmentation, but at variance with those of Kupffer§ and 
Hoffman. 1 1 The cells of fig. 1 are large, and become repeatedly divided 
till they form such a blastoderm as in fig. 2. Coincident with the 
division of the blastomeres, the blastodermic area is extended, and in fig. 
* I have to thank Mr P. Jamieson, Assistant Naturalist to the Board, for his 
valuable assistance in the technique, and Mr F. G. Binnie who drew the figures from 
my preparations. 
t M'Intosh, W. C, and Prince, E. E, 'On the Development and Life-histories of 
the Teleostean Food and other Fishes,' Trans. Roy. Soc, Edin., vol. xxxv., 1890. 
X Cunningham, J. T., 'The Eggs and Larvse of Teleosteans,' Trans. Roy. See., 
Edin., vol. xxx. 
§ Kupffer, C, ' Die Entwicklung des Herings in Ei/ Jahresb. der Comm. dent. Meer 
in Kiel, 1874-76. 
II Hoffman, C. K., Zur Opt. der Knockenfische, Archiv f. mikros. Anatomie, 
vol. xxiii. 
