452 SOME RESULTS OF THE INTERNATIONAL FISHERY INVESTIGATIONS. 



eggs of the herring are of the demersal type, and when spawned by 

 the parent sink to the sea bottom, where they adhere to whatever 

 objects with wliich they come into contact. Upon tliis difference 

 depend differences in the further distribution and development of the 

 two classes of eggs. The pelagic eggs are drifted anywhere in the 

 upper layers of the sea, according to the force and direction of the sur- 

 face drift of the water, whether the latter be due to tidal streams, to 

 the influence of prevailing or exceptional winds, or to the larger 

 movements of sea water which we have been considering as hydro- 

 graphic events. These passive migrations carry pelagic fish eggs from 

 the regions inhabited by the parent fishes at the spawning seasons into 

 others where the conditions influencing their further development may 

 be very different, and it is in respect of this influence upon fish eggs 

 and their development that hydrographic investigation may be ex- 

 pected in the near future to be of much service to the fishery 

 investigators. Demersal eggs, on the other hand, being deposited in 

 the regions chosen by the parent fishes, and at the bottom of the sea, 

 where hydrographic changes are less violent, are assured of more 

 constant conditions for their development. It is probably because of 

 these facts that the great summer herring fishery of the East British 

 coast waters is so constant in its appearance and duration ; and to them 

 is due also the well - marked variations which herring exhibit in 

 different parts of this extensive area. " llaces " of herring, if such 

 really exist, are probably due to the fact that the various herring shoals 

 frequent the same sea areas from year to year, and that their eggs 

 develop in the regions where deposited. 



The development of the eggs of the various species of food fishes, and 

 the subsequent life history of the larvae, which hatch out after a fort- 

 night or so of incubation, have been worked out in considerable detail in 

 the past. The tracing out of the development of the embryo and 

 larva was a task of no great difficulty, and could easily be carried out at 

 the marine laboratories, even at the small ones, with no great wealth of 

 apparatus. All that was necessary was to procure the fertilized eggs of 

 the species to be investigated. This was usually done by " stripping " 

 mature fishes, that is, by expressing the ripe eggs and spermatozoa 

 from the reproductive organs and then keeping the eggs and larvae 

 in running sea water in small tanks and patiently studying tlie changes 

 taking place during the developmental period. So we find in the 

 literature, Englisli, Danish, Norwegian, and German, detailed descrip- 

 tions of the life history of most edible fishes during the first few weeks 

 of life. Comparatively little has been added to this literature by 

 the International investigations of the last four or five years. It is 

 with regard to the further life history of the fish that most recent 



