OOODRRING IN THE NEIGHBOURHOOD OF PLYMOUTH. 19 



becomes distinct, and especially after the yolk is completely covered 

 by the blastoderm, the groups of oil-globules are mostly aggregated 

 on each side of the embryo, though there are a few groups at other 

 parts of the surface of the yolk (fig. 11). 



I have only, on account of the great scarcity of my material, been 

 able to examine two stages in development from artificially fertil- 

 ized eggs. Fig. 10 shows a living but unfertilized ovum, di'awn on 

 March 8th. The development of a fertilized ovum examined on 

 the same day had evidently been very slow, owing to the low tem- 

 perature to which it had been exposed ; the temperature of the 

 surface sea-water in which the ovum was fertilized was 7*7° 0., 

 and as the jar had been kept on board the trawler until shortly 

 before the time when the ovum was examined, the temperature of 

 the water containing the ovum was probably even lower than this 

 during the two days. 



Fig. 11 is taken from another ovum fertilized on May 16th, and 

 drawn three days afterwards, the temperature at fertilization having 

 been about 10 C, and in the jar containing the ovum during the 

 time it was on board the boat probably somewhat higher. At this 

 stage the enclosure of the yolk by the blastoderm has been com- 

 pleted, the embryo is distinctly formed, the optic vesicle is present, 

 and the vesicle at the posterior end, known as Kupffer's vesicle, is 

 fully developed ; this vesicle is unusually large. Black chromato- 

 phores have appeared on the sides of the embryo and on the surface 

 of the yolk, the former being still in the form of dots, the latter 

 dendritic or stellate in shape. 



It is evident that the peculiarities of the sole's egg enable it to 

 be easily recognised when taken in the open sea in the tow-net. 

 Twice I obtained specimens in this way. The first time was on 

 March 16th, 1888, from a tow-net worked between the Tinker and 

 the Knap buoys just outside Plymouth Breakwater, just after high 

 water, when the temperature at the surface of the water was 6'6° C. 

 There were three ova altogether, one of which is shown in fig. 12. 

 The diameter of this was 1'47 mm. The individual oil-globules and 

 the vitelline segments were of somewhat larger size than in the artifi- 

 cially fertilized ova, but this is probably a mere individual variation, 

 and there can be little doubt that the ova belonged to Solea vulgaris. 



The second time was on April 18th from a tow-net worked on the 

 east side of the Sound, when I found only a single ovum, which is 

 figured in fig. 13. This ovum was in the same stage as the artifi- 

 cially fertilized one shown in fig. 11, but it is figured in a different 

 position. It agrees in structure exactly with the ova taken directly 

 from the parent fish, but its apparent size in the figure is greater. 

 It was drawn under a cover-glass, and in this condition measured 



