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 gome parts 
of the coast, moreover, the limits of the normal spawning period of the 
herring may be earlier or later than what I Lave 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 mos$ 
other species. 
5,—Tue Duration or Empryonic 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 larve 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. 
r avaknwa tt Number of 
Place. Season. eet Days to Authority. 
5 Hatch. 
| 
Firth of Forth, February, March, . (40-41) 25-30 Allman. 
Clyde, . March, . . 41-44 18-22 Ewart. 
“Pee March-April, (40 -45-5) 26 Dannevig. 
Plymouth, January, 48 12-14 Cunningham. 
Zuiderzee, April, 48°9 12 Hoffmann, 
Bohusliin, | Spring, — 24 Malm. 
Norway, : Spring, . - 24 Boeck. 
Stockholmliin, —- . a 14 Sundevall, 
Morko, . : ; = 14 Ekstrém. 
Northumberland, . | August, 52-58 8 9 Cunningham. 
Denmark, “tel oh oe — 8-10 Kroyer. 
Clyde, | September, . 54 8-10, 18 Ewart. 
Stockholmlin, | August, 57-59 6-8 Sundevall. 
Kiel, Autumn, 50-51 11 Meyer. 
; | Spring April, 644-68 8-10 aA 
*. <5 ‘ 51°8-53 6 11 “i 
iy | . 35°6 28-34 
39 (Pas 32 47 33 
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°12 46°38 51:2 54:1 551 54h 5S 47°8 44-4 
Bottom, . 42°38 41°0 39°9 41°9 44:8 46°6 50°0 52°9 53m 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 
