THE COD FAMILY. 275 



at 2,000,000, while Olsen gives 7,000,000. During this time 

 the ripe adults are said to refuse all food and to take up their 

 habitat at the bottom, so that they may then be freely caught 

 in the trawls. 



The Scandinavian authors 1 state that during the greater 

 part of the year the hake lives alone, or follows the herring 

 and mackerel in companies, but in the spawning-season it 

 collects in fairly large shoals at the spawning-places. In the 

 Cattegat the spawning-season is in the middle of July, and it 

 is said annually to frequent the same area. 



The egg (Plate III, fig. 4) is pelagic, and by no means large 

 for the size of the fish, having a diameter of '9 to 1-03 mm. 

 This is a size closely similar to that of the poor-cod. A large 

 oil-globule is present, and in this feature the hake resembles 

 the ling and the rock lings, and differs on the other hand from 

 the true gadoids, such as the cod, the haddock and the whiting. 



Dr Raffaele succeeded in artificially fertilizing the eggs of 

 this species in early May and he gives the duration of develop- 

 ment in the egg as 60 to 70 hours. This is an extremely rapid 

 course of events and is no doubt due to the small size of the 

 eggs and to the high temperature of the water at Naples during 

 that month. 



The egg of the flounder hatches in about 5|- days, at 8 C., 

 a temperature which is about the mean for the month of May 

 off our coast, and as the egg of the flounder is about the same 

 in bulk as that of the hake, it is not unreasonable to assume 

 that the egg of the latter would take about 5| to 7 days in 

 these northern seas. The period of incubation of the flounder's 

 egg is reduced to 3 days at a temperature of 12 C., and at the 

 same rate of reduction a period of 70 hours would correspond 

 with a temperature of 13 C. or 55 F., by no means a high 

 temperature for the Mediterranean waters. The close agree- 

 ment in size of the eggs of the hake, flounder and poor-cod will 

 be readily observed in the Table of the sizes of the various eggs. 



In Plate III, fig. 4, is seen the embryo stretching across 

 the yolk in the egg. The black pigment is scattered over the 

 yolk-sac in stellate spots and a few also appear upon the 



1 Op. cit. p. 518. 



182 



