I Marine Copepoda 45 k 



feet, as is the case in other species. In the males of Th. longispinosus and 

 thompsoni, there are only three si on the Re 3 of p 1, in addition to the st, 

 according to Giesbrecht. 



Fig. 70. Th. bernardensis. Terminal portion of left antenna; only the 

 primary bifurcation of the branched setae is shown. 



The material obtained by the Canadian Arctic Expedition constitutes an 

 imperfect index to the wealth of elemental life in the northern waters of Canada. 

 The Copepods, as a class, provide fish food for food fish. There is an inexhaust- 

 ible supply of this fish food in the Arctic ocean, whence it filters down into the 

 northern seas, where commercial fisheries are carried on. By tracing out 

 the southern extension of arctic and sub-arctic forms, a great deal has been 

 accomplished in giving precision to problems which await solution in the North 

 Atlantic. Similar exploratory and experimental work is required for the North 

 Pacific. In this way materials would be forthcoming which would enable the 

 age-composition of the different colonies of organisms on the sea-floor to be 

 made out. Equipped with such data we should be able to foretell the probable 

 incidence of lean years in the fisheries. With this information at their disposal 

 the capitalist corporations would be able to curb their tonnage so as to maintain 

 an economic equilibrium between the market and the deep sea. This is what 

 biological work can do for the deep sea and other fishery interests. Leaving 

 out of consideration the salmon family and some other anadromous fishes, 

 science cannot effectively replenish the stock of fishes in the sea, but it can claim 

 to predict the periodicity of fluctuations when the necessary data have been accu- 

 mulated after many years. 



No epidemics affect the plankton, but we know that higher animals are 

 liable to various disorders and derangements whereby their numbers are reduced. 

 The presence of an abundant food-supply does not unfailingly attract a multi- 

 tude of feeders, and this fact, well-known to marine biologists and other natural- 

 ists, but not so well known to those who have had no actual experience in the 

 matter of the interdependence of organisms, indicates that while there is no 

 limit to the supply of primary food-stuffs in the sea, there are limits, in some 

 cases very narrow, in others very wide, but always very definite, to the valuable 

 species which subsist directly or indirectly upon this food. 



Whilst investigating the distribution and periodicity of the food-organisms, 

 the biologist is brought into contact with the feeders, and though his methods 

 of extracting secrets from the sea may be slow, yet they are sure. Not sensa- 



