121 



March 24. — Examined the eggs ; found segmentation completed, the blastoderm 

 commencing to spread over the yolk. Temperature of water in the hatching 

 jar, 50°- 1 F. (10"-1 C). 



March 25. — Blastoderm covering three-fourths of the j'olk. Temperature the 

 same, 



March 26. — The yolk completely enveloped by the blastoderm, stage shown in 

 PI. XV, Fig. 4. 



March 27.— Eggs all dead. 



March 29. — Six soles' ova obtained from surface of the sea in stage just after the 

 closing of the blastopore, that is, after the' envelopment of tlie yolk by the 

 blastoderm. Placed in a small jar with water at 50°'3 F. to 53°"6 F. (10°'2 to 

 12° C). 



April 5 and 6. — Three of the above eggs hatched. 



The eggs last mentioned were at about the same stage when first obtained as the 

 previous lot when they died. It may be inferred therefore that at the temperature 

 above given, about 50° to 53° F. (10° to 12° C), soles' eggs would hatch ten or 

 eleven days after fertilisation. The following experiment is more complete : — 



April 11. — 12.5 a.m. Several hundred ripe eggs obtained from soles trawled 

 south of the Wolf Eock : artificial fertilisation attempted with testes taken from 

 the males and crushed in the water. Temperature of surface water of the sea, 

 48°'5 F. (9°-2 C). 



April 13. — Eight of the above eggs found to be fertilised and developing; 

 temperature of the water in the bottle in which they were carried, 9'5 C. 

 These were transferred to a small jar in the Laboratory ; temperature, 10°'0 C. 

 Density of the water brought from south of Wolf Eock, 1'0271. Density of 

 aquarium water, 1'028. 



April 16. — Two of the eggs killed for investigation; one died. Temperature in 

 aquarium, 9°'0 C. 



April 17. — ^Temperature in aquarium, 9°-2 C. 



April 18. — Temperature in aquarium, 9°'7 C. 



April 20. — Two of the eggs hatched out. 



Thus two of these eggs hatched on the tenth day after fertilisation in water at a 

 temperature of 48°-0 F. to 50°0 F. (9° to 10° C). Now, as I have shown, the spawning 

 period of the sole terminates sooner or later according to the temperature of the sea, 

 and scarcely any ova are shed after the temperature has risen to 50°'0 F. At the 

 beginning of the spawning period, in the latter half of February, the temperature is 



B 



