0/ the Fishery Board for Scotland. 103 



Above that a layer of gravel supported two layers of sand. The latter were 

 each about four inches thick. The lower layer was a coarse sand, while the 

 upper was a fine sand. The two grades were separated by means of a sieve 

 from mixed sand. When the filter became dirty it was easily refilled. 

 Sometimes it was sufficient to replace the upper sand layers with fresh 

 material. 



The cooling of the water was, on the advice of Dr. Fulton, arranged in the 

 following manner. The apparatus consisted of a wooden trough 7-|- feet long 

 by 1 foot wide by 10 inches deep (see wood-cut) In the trough a number 

 of tins filled with ice, or ice and salt (I), were fixed. They were on guides 

 attached to the two sides alternately, so as to cause the current of water to 

 flow in a zig-zag course. As many as twelve tins, measuring 3 to 5 inches 

 in width, about 10 inches wide, and 14 inches high, were placed in the 

 trough. The partially cooled water passed out from the bottom of the 

 trough at (i) into the hatching apparatus. It then met a series of two or 

 three tins filled with ice. For a short time at the beginning of the experi- 

 ment a mixture of ice and salt was put into the tins. Passing these, it 

 entered the sheet-steel egg-box (E), which was surrounded with ice (J), and 

 which had a lid filled with ice. The water then proceeded to another egg- 

 box or into a hatching-box (H), as shown in the drawing. In this case the 

 hatching-box contains spawn on gravel (gr). The arrow denotes the course 

 taken by the water. The letter (o) denotes the overflow. 



The temperatures were taken by the attendant for the most part, but from 

 time to time by myself. The observations were made, with few exceptions, 

 from three to seven times in the twenty-four hours. 



Lot I. — February 18, — The water in the barrel in which the spawn was 

 brought to Aberdeen was dirty ; it had been got at low water in Anstruther 

 harbour. On arrival the temperature of the water was 5 '6° C, with a 

 specific gravity of 27'2. The temperature of the water in the hatchery was 

 4*4° C, and the specific gravity 27 •2. The plates were left in this running 

 water overnight. 



February 19. — The plates were taken out of the water at 3-2° C, 



and put directly into a cooled egg-box iii which the water was at 0-4° C. 



Lot II. — February 19. — When this lot arrived at the Laboratory the 

 water in the barrel was at 6° C. The plates were put into running hatchery 

 water at 3-6° C. till next day. 



February 20. — The plates were transferred from the water at 



3*8° C. to egg-boxes at 0° C. and — 1° C. respectively. 



Lot III. — February 19. — On arrival the eggs were put into the hatchery 

 water at 4° C. 



February 20. — The plates were transferred at 8 a.m., directly from 



the water at 3*8° C. to the cooled water at 0° C. and — '4° C. 



An egg was examined shortly after the plates had been put into the cooled 

 water. It was in the blastodisc stage (fig. 1). The zona was torn at the 

 point where the egg had adhered to the plate. A small piece of weed was 

 adhering to the zona. 



At 11 a.m. a box containing one plate of Lot III. was taken out of the 

 cooling apparatus when the water was at — 1*8° C. The box was left 

 standing to permit of the water warming up. At 2.20 p.m it was at 1° C, 

 and by 7.45 p.m. it had reached a temperature of 5*4° C. A current of 

 water at b'^" C. was then started flowing through the box. This box 

 received water at the ordinary temperature after this date. 



On February 21 a plate each from Lots I. and II. were put into this 

 box. That from Lot I. was taken from 0-3° C. and put straight into water 

 at 1-4° C. An hour-and-a-half later the water registered 4-6° C, and the 

 plate was then transferred to the tin at 6*8° C. The plate of Lot II. was 

 shifted directly from water at -4° C. to water at 2° C, and then from 2-1° C. 



