202 TRANS ACTIQNS LIVERPOOL BIOLOGICAL SOCIETY. 



organisms occurred on the 21st, and caused the increase in 

 the volume of the catch although not in the number of 

 organisms caught. 



In the case, on the other hand, of a sudden rise early 

 the following month from 7 c.c. on May 4th to 20'5 c.c. 

 on May 10th, the number of Diatoms rose from 115,450 

 to 2,268,750, which quite accounts for the increase in 

 volume of the catch, and this was in fact the beginning 

 of the vernal Diatom maximum, and the numbers of c.c. 

 went on in the next few days to 35' 7, 42' 8, etc., all caused 

 by Diatoms in tens of millions. As an example of how 

 thick the water was with phytoplankton. at the time, it 

 may be stated that on May 16th, when the largest 

 horizontal hauls were obtained (42*8 in coarse, and 60'2 

 in the fine net), the vertical net hauled through only six 

 fathoms gave 17' 2 c.c. (a very large haul for the vertical 

 net) and contained nearly three millions of Diatoms. As 

 a contrast to that, we have a month later the vertical net, 

 on June 15th, giving 16 c.c. (nearly the same volume of 

 catch) with only 8,200 Diatoms. On looking into the 

 specific details the cause is seen to be the great increase 

 in the number of Copepoda on the latter date. 



Bay Diatoms. 



The following notes as to the occurrence of the 

 Diatoms at Port Erin at the time of the vernal maximum 

 were taken at the time of collecting, but have been revised 

 and added to since as a result of examining the catches in 

 detail : — 



May V&th. — The Yernal Diatoms now appeared in 



quantities (calm weather with a marked rise in 



temperature). 



May l§th. — Tow-net gatherings large, and consisted 



almost entirely of Diatoms (weather continues 



