THE HERRING FAMILY. 409 



shells of living crabs ! The adults were plentiful on the 

 spawning-ground from the 6th of March to the 13th, and 

 disappeared on the 25th. When spawning the herrings lie in 

 tiers, covering square miles of sea-bottom and so close to the 

 ground that the fishermen have to practise a peculiar mode 

 of fishing in order to take them. The shoal rapidly disap- 

 pears after spawning. They found the period of incubation to 

 be from 25 to 30 days, and that there are two spawning- 

 periods, one in the spring, February and March, and another 

 in the autumn, August and September. Similar observations 

 have been recorded by later workers. 



In 1 874, under the German Fish-Commission, there appeared 

 a series of investigations on the herring. Dr A. H. Meyer 

 made some valuable observations upon the eggs and young. 

 He found that at a temperature of 53° F. the eggs hatched in 

 about 8 days, whilst at 38° F. the period of incubation was 

 prolonged to 40 days. He concluded that the disappear- 

 ance of herrings from their usual spawning-banks has perhaps 

 sometimes resulted from a lowering of the bottom-temperature. 

 He also showed that the length of the fry when hatched varied 

 with the time required for development ; fry measuring ^ in. 

 (.5 '8 mm.) when development was rapid, but |in. and having a 

 smaller yolk-sac when prolonged. Some embryos, hatched in 

 14 days, were kept in Kiel Bay and were found to have lost 

 their j'olk in 3 days. Other observations of Di- Meyer and 

 their bearing are mentioned in the chapter on Rate of Growth. 

 Dr C. Kupffer gave a detailed description of the developmental 

 changes during the embryonic and larval j)eriods, and from his 

 account we shall quote largely. 



Dr Heincke attempted to show that the autumn-herring 

 is anatomically distinguishable from the winter one, whilst 

 Ljungman, acting under the Swedish Government, besides 

 corroborating several of the observations of his predecessors, 

 found that herrings avoided light and their movements were 

 therefore largely determined by the diurnal cycle. He also 

 ascertained that during the prevalence of sea-winds the shoals 

 shun the shore, approaching the land however when the winds 

 blow offshore. 



In 1878 certain investigators under the United States Fish- 



