410 THE HERRING FAMILY. 



Commission succeeded in artificially fertilizing and hatching the 

 spawn of the herring. 



In 1881 Hoffmann published an account of the development 

 of the herring founded on observations on eggs from the Zuyder 

 Zee. Kupffer's description has been largely corroborated by 

 Brook and other British workers, and a few notes upon the later 

 stages have been recorded by Holt and others at St Andrews 

 Marine Laboratory. 



This very brief resume of the literature upon the develop- 

 ment of the herring is not by any means exhaustive, but will 

 serve to indicate the fact that contributions to our knowledge 

 have been made by a great number of observers of different 

 nationalities. It is scarcely needful to state that the accounts 

 do not all agree, but the points of difference are less connected 

 with the observed facts than with the inferences drawn therefrom. 



The sexes are about equal in number, though if anything 

 the males are slightly in excess. A single female will carry on 

 an average about 30,000 eggs, though as many as 47,000 have 

 been recorded. This is not an excessive fecundity and is much 

 below that of pelagic-spawning fishes. The time of spawning 

 both of the spring- and autumn- herring shows considerable 

 variation at different parts of the coast. For example, the 

 autumn spawning-period on the east coast of Scotland is 

 August and September, and off Yorkshire it is in October. As 

 far south as Suffolk and Kent it is as late as November. 



The egg of the herring (Plate IV, fig. 24) is from '92 to 

 1 mm. in diameter, some are as small as '85 mm. Boeck, 

 however, found that the Norwegian herring had an egg of at 

 least 1'5 mai. diameter. The membrane surrounding the egg 

 is tougli and elastic and is multilaminar ; a radial striation 

 can be observed, as in many other species. Most authorities 

 agree that the membrane consists of two layers (Kupffer, Boeck, 

 Hoffmann), and the last-mentioned gives the thickness of the 

 outer layer as '01 mm., that of the inner '022.5 mm. Both ai'e 

 perforated by fine canals, those of the inner layer being the 

 finer. The two layers may be easily separated by special 

 methods. Hoffmann interprets them as integral parts of the 

 one egg-membrane {zona radiata), and gives reasons for sup- 

 posing that this zona is a true vitelline membrane, which could 



