52 Proceedings of the Royal Physical Society. 



was immediately conveyed to the middle of the channel and 

 deposited in 98 fathoms water, about three miles off Tarbert. 

 The tank was lowered by means of a strong manilla rope, to 

 the upper end of which a large cask was attached to serve as 

 a buoy. The surface temperature was 54° Fahr., the bottom 

 temperature was 49° Fahr. The bottom around the tank 

 was chiefly composed of mud. On the 24th — i.e., thirteen 

 days after fertilisation, and eight days after the eggs were 

 deposited in 98 fathoms water — the tank was raised. On 

 examining the glass plate, it was found a number of the eggs 

 in the centre had been destroyed by a fine coating of mud, 

 which had entered through the hair-cloth screen, while those 

 near the margins contained vigorous embryoes almost ready 

 to hatch ; in. a few cases hatching had taken place. The 

 average bottom temperature while the eggs were deposited 

 was 49 '3° Fahr.; the average surface temperature, 54° Fahr,, 

 the difference being 4*7°. This is a much smaller difference 

 than was expected, and may be accounted for by warm 

 bottom currents running along the deep narrow channel 

 which extends from opposite Tarbert towards Ardrishaig. 

 The difference of 4*7° during the eight days which the eggs 

 were deposited delayed hatching for about five days. 



This experiment clearly shows that the only difference 

 between the hatching of herring ova in deep and shallow 

 water is one of time, and we may now safely conclude that 

 if herring deposit their eggs on suitable ground, in any 

 depth of water not exceeding 100 fathoms, that they will 

 undergo development. It is conceivable, however, that the 

 depth of the water in which the eggs are deposited may 

 have some influence on the time of spawning — in other 

 words, on the fishing season ; and the immature condition of 

 the fish caught in August during recent years may be ac- 

 counted for in this way. If the herring which formerly 

 spawned on the inshore banks of the Moray Firth in from 

 10 to 20 fathoms water now spawn oif shore in from 40 to 60 

 fathoms water, the hatching will be delayed for several days, 

 and maturity will not be reached as early as formerly. This 

 is an argument in favour of beginning the herring fishing 

 later in the season than at present. 



