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



speckled with opaque yellowish-white pigment. This pigment is arranged in interrupted 

 touches on the body and marginal fin (dorsal and ventral), behind the yolk-sac, so that 

 the pleuronectid character is early indicated. Moreover, the presence of pigment at 

 the extreme margin of the fin, both dorsally and ventrally, gives great apparent depth to 

 the body of the fish. The yolk-sac is comparatively large and globular, sustaining the 

 larval fish readily in the water, either as in ordinary cases (sac uppermost), or suspended 

 from it tail downward. Occasionally it remains in a vertical position with the head 

 downward. The large and rounded condition of the yolk-sac causes the active little fish 

 to roll over during progression, so that it often advances in a screw-like fashion. While 

 in lateral view the yolk-sac is somewhat ovoid, it is quite circular when seen either from 

 the front or the rear (PI. XXIII. fig. 10). The same condition probably causes the larva 

 to make frequent gyrations. It would appear to be one of the most restless of the group, 

 seldom remaining quiescent under examination more than a few seconds. It is not quite 

 3 mm. in length. The oil-globules form two main groups, one series running from the 

 heart obliquely backward to the region of the pectoral fin, the other at the posterior 

 part of the yolk, and extending ventrally along the posterior border (see fig. 13, PI. XVIL). 

 They slightly vary in different specimens. One or two isolated groups also occasionally 

 occur along the ventral border. All retain their periblastic position. No pigment other 

 than the superficial chromatophores exists in the eyes. 



The vesicular condition of the yolk is not readily seen after hatching, though it can 

 be made out by manipulation of the light, or in favourable positions. The vesicles 

 appear to be flattened out at the margin of the yolk. In a specimen of the first day, 

 peculiar vesicles, having a faintly pinkish hue like those of the blastodisc of the haddock, 

 were visible on looking down on the yolk-sac of the larval fish floating head down- 

 ward (PI. XXIII. fig. 10). They were grouped in the neighbourhood of the posterior 

 oil-globules, and occurred nowhere else in the yolk. They differed in appearance 

 from the ordinary vesicles at the border of the yolk, and resembled peculiarly modified 

 protoplasm. Their globular condition was distinctly visible during the motions of the 

 larva, and they were situated in the transparent yolk within the oil-globules. One of the 

 vesicles presented a series of minute granules in its interior. They were observed subse- 

 quently in various specimens. 



One example presented a vesicular process over the brain, so that it had a hooded . 

 aspect, but this enlargement appeared to be abnormal. 



On the second day the yolk has considerably diminished, and the posterior border 

 carries the groups of oil-globules forward with it, leaving a larger space between it and 

 the vent, while the pericardial chamber has become distinct in front. Minute pigment- 

 specks now appear in the eyes. The peripheral segments of the yolk are still indicated. 



On the fourth day the yolk has still further shrunk. The cavity of the mouth is 

 formed, though no external aperture yet exists. The vent has not yet opened, indeed 

 the gut terminates a little within the margin of the fin. The clear vesicles observed in 

 the yolk of the former specimen were still visible, and one had a minute globule of oil in it. 



