392 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



It is interesting- to notice how these species almost 

 invariably come in the same order year after year. This 

 result tends to give one confidence that our methods are 

 fairly reliable, and are leading us to what we may be 

 entitled to regard as truths of nature, and not merely 

 the hap-hazard outcome of experiments which might have 

 come out differently had the experiment been performed 

 otherwise. A primary purpose of plankton experiments 

 under new conditions ought always to be to eliminate 

 fallacies due to the artificial factors of the experiment 

 and get down to the fundamental facts. 



Cladocera. 



In 1912 Podon intermedium, first appeared in the 

 Bay on March 8th, attained its maximum on May 17th 

 (3,900), and died down by the end of October. The 

 numbers are generally in the tens or few hundreds, so 

 that one could rely upon catching, say, from 50 to 200 

 specimens in an average haul between April and 

 September. 



Evadne nordmanni was present from March 18th to 

 August 1st, and reached its maximum at the same time 

 as Podon with 7,900, and 6,500 a few days later. The 

 usual hauls are of much the same character as those of 

 Podon, but the occurrence is practically restricted to 

 April, May and June. 



Last year the maximum of both these forms was in 

 September, and did not reach quite so high a point as in 

 1912. The group then is essentially a summer one, and 

 in this locality seems to have been on the increase during 

 the last few years. The difference, however, from year 

 to year is not very striking, and the general form of the 

 curve remains fairly constant. The Cladocera may be 

 regarded as having their utility in nature in making a 



