48 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



supposes never really happens; that the Phyto-Plankton 

 never exhausts any food constituent, and that it develops 

 just such a rate of reproduction as will compensate for the 

 destruction to which it is subjected. This destruction he 

 holds is due to two causes : currents carrying the Diatoms 

 to unfavourable zones or localities, and the animals of the 

 Plankton which feed on them. The quantity of Phyto- 

 Plankton present in a sea will then depend upon the 

 balancing 1 of the two antagonistic processes — the repro- 

 duction of the Diatoms and their destruction. We require 

 further knowledge in regard to their rate of reproduction 

 and the amount of the destruction ; but it has been 

 calculated that one of these minute forms, less than the 

 head of a pin, dividing into two at its normal rate of five 

 times in the day, would at the end of a month form a mass 

 of living matter a million times as big as the sun. The 

 destruction that keeps such a rate of reproduction in check 

 must be equally astonishing. It is claimed that the 

 " Yaldivia " results, and observations made since, show 

 that the most abundant Plankton is where the surface 

 water is mixed with deeper layers by rising currents. 

 Nathansohn, while finding that the hour of the day has no 

 effect on his results, considers that the development of the 

 Phyto-Plankton corresponds closely with evidence of 

 vertical circulation. Like some other workers, he 

 emphasises the necessity of continuous intensive work in 

 one locality. The " Challenger " and other great exploring 

 expeditions forty years ago opened up problems of 

 oceanography, but such work from vessels passing 

 rapidly from place to place could not solve our present 

 problems — the future lies with the naturalists at biological 

 stations working continuously in the same locality the year 

 round. As an example of the complexity of such problems, 

 there seem to be two kinds of Diatom maxima found by 



