112 Transactions of the Royal Canadian Institute 



one direction, then in another. There can be no doubt but that the very- 

 considerable fluctuations in their numbers is caused by their being 

 carried into the bay in varying quantities from the adjacent Gulf of 

 Maine. Currents sufficient for this have been shown to exist on the 

 Nova Scotia side of the mouth of the bay. Herring larvae from eggs 

 spawned outside the bay have been found carried in along the shore, 

 and the drift bottle experiments conducted by Dr. J. W. Mavor have 

 definitely proved the same movement to occur. The tributary bays 

 and basins, although somewhat more successful than the Bay of Fundy 

 itself as breeding grounds for Sagitta, do not provide sufficient young 

 to account for the enormous numbers of adults that are frequently found 

 there. 



The sagittid population of the Bay of Fundy is kept up therefore, 

 almost wholly by indraughts from the Gulf of Maine. 



Conclusions. 



(1) Sagitta elegans breeds successfully in the Magdalen shallows of 

 the Gulf of St. Lawrence, as shown in the regular advance in develop- 

 ment of the eggs and young with the progress of the season. 



(2) It does not breed successfully in the Bay of Fundy, as shown by 

 the predominance of early embryonic stages throughout the season and 

 by the scarcity of young. 



(3) The data of neither the temperature, the salinity, not the density, 

 afford grounds for considering any one of them as the factor responsible 

 for this difference between the regions. Some factor associated with the 

 general difference in conditions of the two regions must be sought. 



(4) In the Bay of Fundy, the very limited success in breeding is 

 correlated with the attainment of a high temperature, with the develop- 

 ment in deep water of a special surface layer, or with the presence of 

 estuarial conditions. 



(5) The population of adult Sagittae in the Bay of Fundy is too great 

 to be the result of local breeding, and must be considered as the result of 

 indraughts around the southern end of Nova Scotia from somewhat dis- 

 tant waters. 



REFERENCES 

 Huntsman, A. G. 



1919. Some quantitative and qualitative plankton studies of the 

 eastern Canadian plankton. Canadian Fisheries Expedition, 1914- 

 1915, pp. 405-485. 



Vachon, a. 



1918. Hydrography in Passamaquoddy bay and vicinity, New 

 Brunswick. Contr. Can. Biol. 1917. pp. 295-328. 



