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Part III — Fifteenth Annual Report 



9| days to hatch, those of the whiting G J days, the eggs of the plaice 

 10.V days, and the eggs of the flounder 3j days. 



From a comparison of these facts with the months during which the 

 spawning of the various species goes on, the generalisation made above 

 becomes clear, namely (1) that the eggs of those species which spawn 

 early in the year will be subjected to the action of the current for a con- 

 siderably longer time than those which spawn later ; (2) that the eggs 

 of any given species which are shed at the commencement of the 

 spawning season of that species will be subjected to the action of the 

 current for a longer period than those which are shed towards the end 

 of the spawning period. 



Thus, under natural conditions in the sea, the eggs of the plaice, a 

 fish which spawns early, will take about twenty-three or twenty-four 

 days to hatch in February and March, while those shed at the end of 

 the spawning season, in May, will hatch in about sixteen days. The 

 eggs of the cod and haddock shed at the beginning of the spawning 

 season, and up to nearly the end of March, will take about twenty days, 

 and towards the end of the spawning time, about twelve or thirteen 

 days before hatching occurs. The hatching period of the eggs of the 

 whiting will vary from about sixteen days at the beginning of the 

 spawning season to about six at its close ; that of the saithe will vary 

 from fifteen or sixteen days to eleven or twelve. Among species which 

 spawn in the summer the period is much shorter. Turbot eggs, which 

 are shed from April to July inclusive, probably take from about eleven 

 or twelve days at the beginning of the season to about five days towards 

 its close ; and the same remarks apply to the eggs of. the ling. The fact 

 discovered by Holt, and confirmed by Canu and MTntosh, that the eggs 

 of the turbot sink during development in water of ordinary specific 

 gravity, will probably cause the period of hatching to be rather more 

 •prolonged in this case, because the lower layers of water are colder 

 during the spawning season of this fish. Dannevig has, however, 

 shown that the specific gravity of the turbot's egg during development 

 does not exceed 1028, in which case in the open sea it will not sink very 

 far. The eggs of the gurnard, which are shed from April to August 

 inclusive, require about fourteen or fifteen days to hatch at the com- 

 mencement of the spawning season, and about eight or nine days 

 towards the close of the season. The eggs of the sprat, which are small, 

 are shed from the middle of March to the middle of August, and the 

 period of hatching will range from about eight or nine days to about 

 four days at the end of the season. The eggs of the common dab, the 

 smallest of all the pelagic eggs belonging to a food fish, will require 

 about seven or eight days at the end of February, when spawning com- 

 mences, to between two and three days at the close of the season in 

 July. The eggs of the flounder, which are also small, will hatch in 

 about eight days at the beginning of the spawning season in February, 

 and in five or six days towards its close in June. The hatching period 

 of the eggs of the halibut is unknown, for living eggs have never yet 

 been under observation, but judging from the size of the eggs, and 

 assuming (what is not yet satisfactorily proved) that they are shed in 

 the spring, they would probably require four or five weeks to hatch. 



From the facts stated it is evident that the dispersion of the indi- 

 viduals of different species in the egg state by the movement of currents 

 must vary to a considerable degree, and that in some cases the extent of 

 the movement is great. The eggs of the plaice, for example, in the 

 twenty-three or twenty -four days they are floating during development, 

 may travel southwards more than 50 miles — sometimes much more — 



