of the Fishery Board for Scotland. 



303 



and the latter from the spring spawning in the following year by 

 rather more than six months. 



Too much stress perhaps is laid on the fact that spawning herrings 

 may be obtained in most months of the year. There is evidence to show 

 that among several other fishes individuals may be found fully mature 

 at times more or less remote from the spawning period. On some parts 

 of the coast, moreover, the limits of the normal spawning period of the 

 herring may be earlier or later than what I have stated. But that the 

 spawning season is a brief one, both in spring and autumn, is shown by 

 the separation of the age-groups, contrasting in this respect with most 

 other species. 



5. — The Duration of Embryonic Development : Relation to 

 Temperature. 



The period of " incubation," from the deposition and fertilisation of 

 the eggs until the young herrings hatch out, varies according to the 

 temperature of the water, which appears to be by far the most mportant 

 factor. It is desirable to consider the point, because it furnishes a clue 

 to the period when the mass of the larvae escape into the water and begin 

 independent life and growth. 



Many observations have been made as to the hatching of the eggs of 

 the herring at different temperatures, and I append a Table in which I 

 have set down a number of them. 







Temperature. 

 F. 



Number of 





Place. 



Season. 



Days to 



Authority. 







Hatch. 



Firth of Forth, . 



February, March, . 



(40-41) 



25-30 



All man. 



Clyde, . 



March, . 



41-44 



18-22 



Ewart. 



Plymouth, . 



March- April, 



(40-45-5) 



26 



Dannev'g. 



January, 



48 



12-14 



Cunningham. 



Zuiderzee, 



April, . 



48-9 



12 



Hoffmann. 



Bohuslan, 



Spring, . 





24 



Malm. 



Norway, 



Spring, . 





24 



Boeck. 



Stockholmlan, 







14 



Sundevall. 



Morko, . 







14 



Ekstrom. 



Northumberland, . 



August, 



52-58 



8 9 



Cunningham. 



Denmark, 







8-10 



Kroyer. 



Clyde, . 



September, . 



54 



8-10, 13 



Ewart. 



Stockholmlan, 



August, 



57-59 



6-8 



Sundevall. 



Kiel, . 

 > 



Autumn, 



50-51 



11 



Meyer. 



Spring April, 



11 !5 

 )> 5 ) 



64-4-68 

 51-8-53-6 

 35-6 

 32 



8-10 

 11 



28-34 

 47 



The last entries refer to experiments by Meyer. 



It is obvious from the Table that the period of "incubation" varies 

 greatly, and that in the case of spring or winter spawners the duration is 

 much longer than with the autumn -spawning fish. 



At the spawning-grounds near the mouth of the Firth of Forth the 

 temperature of the bottom water in the various months is as follows : — 



Jan. Feb. Mar. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 

 Surface, . 416 40*9 40*1 43-1 46"8 51-2 54*1 55-1 54-1 51-3 47 8 44-4 

 Bottom, . 42-8 11-0 30*9 41 -9 44*8 46*6 50'0 52*9 53*1 51-4 48"6 45.2 



It has been mentioned by Huxley (1) as a point of interest that he 

 met with no case of full or spawning herrings during the solstitial months, 

 viz., June and December ; but it is perhaps of more interest to note that 



