SEA-FISHERIES LABORATORY. 405 



of the movements of fish with the distribution of 

 plankton. There is thus a reasonable probability that 

 an increased knowledge of the minute life of the sea may 

 be directly useful in connection with the regulation of 

 fishing industries. 



The plankton in many cases seems to be the link 

 between the hydrographic changes and the fisheries ; but 

 it must not be supposed that the plankton is in all cases 

 definitely related to the hydrographic data, and that, 

 therefore, a knowledge of the hydrography would suffice. 

 Kofoid showed in 1903 (Plankton of Illinois Kiver) that 

 there are variations in the quantity of plankton which 

 are independent of hydrographic and meteorological 

 conditions. He says: "Somewhat regular alternations 

 " of growth and rest, of fission and spore formation, or 

 " of parthenogenesis and sexual reproduction, are 

 " fundamentally the basis of cyclic movement in 

 " [plankton] production. The amplitudes, and to some 

 " extent the location and duration of the pulses, are 

 " plainly affected by the various factors of the environ- 

 " ment ... by light, temperature, vegetation, tributary 

 " water, various hydrographic factors, and by food 

 " supply, and possibly, also, by chemical conditions not 

 " directly concerned in nutrition, but the available data 

 " fail completely to afford any satisfactory environ- 

 " mental factor or group of factors which stands in 

 " correlation, even remotely obvious with this cyclic 

 " movement in production. I therefore class this 

 " periodic growth, these sexual cycles which cause 

 " volumetric pulses, under the head of internal factors. 

 " The element of periodicity in itself does not seem to be 

 " consequent upon any known external factor." 



E. L. Michael (in his work on the Chaetognatha of 

 San Diego, 1911) supports Kofoid' s view as applying to 



