of the Fishery Board for Scotland. 



179 



through more distant windows in the hatchery. The supply of light was 

 therefore good, and any part could in the daytime be closely examined 

 without interfering with the fry. 



The water supply was taken direct from the harbour, and was in no 

 case filtered. Heavy sediment, bits of sea-weed, etc., were easily separ- 

 ated out. The jar was filled to a height of about ten inches, or a little 

 above the middle, and would contain about ten gallons. The water was 

 generally renewed once a day, or twice, if the weather was hot, in order 

 to prevent the temperature rising too high, which was injurious to the 

 fry and the living food. 



There were therefore no currents similar to those produced by a constant 

 run, but all the same the water in the jar was perhaps never at rest. 

 During most part of the day the temperature of the water was kept below 

 that of the surrounding air. The consequence was, that the glass sides 

 got heated first, and transferred this heat to the nearest layer of water. 

 This would expand as its temperature increased, and consequently rise to 

 the top, being always replaced with water from the lower and inner parts 

 of the jar, where the temperature was lower. This led to a constant 

 movement upwards of the water nearest the glass sides in the daytime, 

 and it was particularly vivid when the sun-rays were allowed to strike 

 the jar. 



On the 6th of May the first experiment was begun when plaice larvae, 

 eight days old, which had just absorbed the yolk, were placed in the 

 rearing jar. Natural food was provided by tow-net collections from the 

 harbour, containing small organisms that were likely to suit. Some of the 

 larvae soon began to feed. When they were sixteen days old it was necessary 

 for me to leave the station, and on my return I found the larvae all dead ; 

 food had been properly supplied during my absence, and I am inclined 

 to think that an excessively high temperature was the cause of death. 

 During the sixteen days, a few of the larvae had attained a considerable size 

 and advance in development, as will be seen from Pi. IV. fig. 2. 



Though the larva3 died, this first attempt was encouraging, and gave 

 good prospect of success, and another hatch was started soon after with the 

 same arrangements. The plaice eggs had been artificially fertilized on 

 April 28th, and hatched on the 9th to the 11th May. Most of the larvae 

 had the yolk absorbed on the 18th, when they were placed in the rearing 

 jar. Tow-net collections from the harbour were supplied twice a day, and 

 the water was at first changed at the same time. About 1200 larvae were 

 put into the jar, and they soon divided themselves into three different 

 classes: — (1) the majority remained persistently swimming near the surface, 

 with the head touching thewaterlineand the body forming an angle with the 

 latter of from 30° to 45°. 



These larvae paid no attention to the food, — if they touched against 

 anything they would swim frightened away, and showed more activity than 

 ever. Though originally richly pigmented (which I consider a sign of 

 well-doing), they gradually became pale, and, giving up this first-men- 

 tioned peculiarity, they soon joined the second class, (2) pale and thin 

 individuals, that occasionally made an attempt to catch small crusta- 

 ceans that appeared near them. They generally remained very quiet, 

 and were mostly near to, or on, the bottom, resting on their head ; in all 

 cases their head was inclined to drop downwards as soon as the body was 

 at rest.* 



* This, I think, is an old experience amongst investigators on this subject, but 

 has been explained differently. Guided by an experiment, I suggested in 1894 [F. 

 B. 12th An. Rep., Part III., page 216], that this sickly state of the fry with the 

 above-mentioned tendencies, was due to want of currents ; and later Prof. Mcintosh 



