DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 837 



Pleuronectes limanda, L. (Dab). — The ripe forms at St Andrews have generally been 

 procured in April and May, but there is no reason to suppose that, as in other marine 

 fishes, they do not overlap these limits considerably. The diameter of the egg is 

 •033 inch, or about '825 mm. 



As an example we may take a series fertilised on April 30 (1885) at 2 p.m. In 

 these ova the peri vitelline space is very small. At 4 p.m. the blastodisc was formed at 

 one pole, and the nuclear zone covered it. At 5.30 p.m. the disc was in the four-celled 

 stage, each sphere with a nucleus. Scattered granules, moreover, occurred on the 

 margin. The morula-stage was reached at 10 a.m. on the second day (1st May), and 

 the granular periblastic zone surrounded the disc, the nuclei being two or three deep. 

 At 12.30 the disc had increased in diameter, showing finer cells in the centre, and 

 larger at the margin. The periblast was broader, and nuclei could be seen under the 

 margin of the disc by tilting the ovum. The disc had still further extended at 3 p.m., 

 and the cells resembled large irregular nuclei embedded in a narrow protoplasmic 

 envelope. On the third day the blastoderm had reached the equator, and the em- 

 bryonic shield was well defined. On the fifth day (4th May) the embryo is fully 

 outlined, and Kupffer's vesicle appears. The cephalic region has increased, but the 

 optic enlargements are not outlined. In certain aspects indications of metameres are 

 observed anterior to Kupffer's vesicle. 



On the morning of the sixth day Kupffer's vesicle had considerably diminished, 

 and about sixteen metameres were indicated, and they extended almost to the head. 

 At 12.30 Kupffer's vesicle had sunk into the tissues of the trunk. The metameres 

 have a rounded dorsal outline. The notochord is distinct from Kupffer's vesicle 

 almost to the pectoral region, and slightly indicated in front of the latter. The lenses of 

 the eyes were faintly outlined at 1 p.m. 



On the seventh day (6th May) about thirty protovertebrse are clearly outlined. 

 The otocysts are small, but well defined, and the cavity is ovoid and limited. The lumen 

 of the mesenteron extends almost to the otocysts, and posteriorly it expands con- 

 siderably, becoming attenuated, however, before ending blindly. The neurula is cleft in 

 the middle line, and rises anteriorly as two bold ridges. Yellow chromatophores (round) 

 are scattered over the head dorsally, and extend almost to the caudal termination. 



On the eighth day the eyes are boldly outlined, and the otocysts have expanded, the 

 oval chamber having increased in length and breath. The lumen of the mesenteron 

 anteriorly appears to be bifid, an arm passing towards each otocyst, but ceasing before 

 reaching the eyes. The protoplasm (periblast) enveloping the yolk has formed many 

 reticulations. At 12 noon the notchord shows lens-shaped cells or vacuoles — 

 partially alternate in arrangment, while at 6 p.m. it is completely segmented by bold 

 fissures. The yellow chromatophores are more distinct, and though irregularly dis- 

 tributed may roughly be described as forming a double lateral line on each side, viz., a 

 dorsal and a ventral. The surface in the cephalic region is rough from papillae on the 

 dorsal and lateral regions. The pectorals are rudely outlined, and the heart appears as 



