28 EEPRODUCTION AND DEVELOPMENT OF TELEOSTEAN FISHES 



the water frora tlie shore, but only added a little of the latter to the 

 water containing them, taking care not to decrease the density so 

 much as to cause them to sink. I discarded the circulation method 

 this time, and left them in bottles of still water. 



On the 27th I was obliged to transfer them to shore water, in 

 which they sank, but I brought them to the surface again by adding 

 common salt. I found on testing I had raised the density to 1030, 

 which was excessive. 



On the 28th I found the temperature of the water containing the 

 ova was 12"1° C. I changed them again into clean water made 

 denser with salt. Many of them were still doing well. 



On the 29th the water was again changed, and the temperature 

 of the old water was 12° C, of the new 11° C. 



On the 30th I fitted up an apparatus on the principle invented by 

 Captain Chester, of the Fish Commission of the U.S.A., and described 

 by A. Ryder in the Commissioner's Report for 1885, p. 499 

 (Washington, 1887). I procured a wooden washing tray with a hole 

 bored in one side near the top, in which hole, by means of a cork, I 

 fitted a glass siphon with its shorter leg inside the tray. In the 

 tray I placed a glass cylinder open both at the top and the bottom ; 

 over the lower opening a piece of muslin was fastened. The eggs 

 were placed in the cylinder, and a supply of water allowed to run 

 at a constant rate into the tray. In consequence the water rose in 

 the tray and the glass cylinder to the height of the hole in the side 

 of the tray when the siphon commenced to act, and the water was 

 drawn off until the level was lowered below the short leg of the siphon, 

 when it commenced to rise again. Clean water in such an apparatus 

 is thus constantly flowing over the eggs, while the latter are only 

 subjected to very gentle motion. 



But it would have been better if I had not been tempted to try 

 circulation again. On the 31st a great number of the ova were dead, 

 and by the evening of this day I could find none alive, and they all 

 had to be thrown away. The damage may have been partially or 

 wholly due to impurities derived from the wooden tray or the 

 muslin, but the probable meaning of the result is that density is an 

 essential condition ; the ova lived and developed four days in still 

 water in which they floated without motion at the surface, although 

 the water for three of these days was shore water made denser with 

 common salt, and when placed in a current of shore water to which 

 no salt was added they died in twenty-four hours. 



In this case the temperatures to which the ova were exposed 

 during the first four days as observed were 13*7 C, 12"1 C, 12 C, 

 and 11° C. The densities were r0267 to 1*030. The temperature 

 of the open sea on May 31st was not more than 9*44 C, and the 



