SEA-FISIIERIES LABORATORY. 203 



calm and the increase in temperature is main- 

 tained). 

 May l\)t}i. — Diatoms occurred in very large quan- 

 tities, especially in the fine net. 

 May 22nd. — Catches rather smaller, but Diatoms 

 still in abundance, even in the vertical net 

 (weather still fine and warm). 

 May 2bth. — Diatoms much less numerous. Fine net 

 had only about one-tenth, or less, of the 

 gatherings on May 19th (no obvious change in 

 weather conditions). 

 All the above large catches of Diatoms consisted 

 almost entirely of species of Chaetoceras. It was not 

 until a week later that Riiizosolenia (chiefly R. semi- 

 spina) made its appearance. It reached its maximum 

 early in June, and then gradually died off. By the 

 beginning of July the Diatoms had practically 

 disappeared. 



The following gives the c^uautity of plankton and the 

 total number of Diatoms present in each haul of the fine 

 net taken during the month of the Diatom maximum : — 



Date. Quantity in c.c. Total Diatoms. 



May 1 2-5 43,.360 



4 1-0 10,610 



„ 10 6-5 525,680 



„ 13 30-2 19,118,000 



„ 16 60-2 .54.U1..500 



„ 19 54-5 34.447,500 



„ 22 30-5 27,775.000 



„ 25 8-3 2,504.500 



„ 29 14-8 22.023,100 



June 1 11-3 4,926,000 



3 24-7 12,943.000 



5 12-7 2,6.56,000 



The sudden rise on June ord is due to Rhizosolenia 

 semispina. The figures given above for May are 

 unusually large, and the increase from about ten 

 thousand on May 4th to over fifty-four millions on May 



