EXPERIMENTS IN THE KEEPING OF PLANKTON ANIMALS. 571 



food-supply {Nitzschia). Notes as to exact dates are incomplete, but the 

 rapidity of growth seems to have become especially apparent during the 

 second week, the Nitzschia then becoming so thick as soon afterwards 

 to necessitate the pouring off and renewal of the water. This was very 

 pronounced in the flasks submerged in the bath heated to about 18°. 

 Under the latter conditions, a flask containing only Nitzschia was re- 

 corded on the 12th day merely as " growing well," and another which 

 was taken over for use in an experiment on the loth day without com- 

 ment was presumably in the same condition. In all of 4 flasks, how- 

 ever, which contained Calanus at this time — 3 specimens in each — 

 the groA\'th became very thick on the 11th or 12th day, and soon after- 

 wards so dense that it was very difficult to discern the specimens. In 

 the same bath wdth these flasks was the one containing 5 Acartiay 

 in which the specimens did well and produced several nauplii, yet in 

 this case the growth was on the 40th day so slight that the Nitzschia was 

 then renewed. Similarly, in all the experiments with Pseudocalanus (4 

 ^^ith Nitzschia) no pronounced growth of the Diatom occurred during 

 the long period for which this species was kept. 



While this overgrowth of food in experiments with Calanus was a 

 serious hindrance and probably interfered considerably with the 

 preservation of healthy conditions, the fact has a greater importance 

 in its bearing on Diatom growth. Further investigations are needed 

 before any very definite conclusions can be drawn from these limited 

 data, but the facts suggest the presence of a strong fertilising 

 action directly or indirectly traceable to the excretory products of 

 Calanus finmarchicus, which, though probably occurring also in other 

 species, seems not to occur in Pseudocalanus, or, judging from one 

 experiment, in Acartia. 



The water used in all these experiments was " outside " water, some- 

 times sterilised, always with the addition of one-third Miquel-Allen 

 solution, that is to say, in the proportions of 2 c.c. of Solution A and 1 c.c. 

 of Solution B to 3 litres of sea- water, the water being then filtered through 

 a Berkefeld filter. How far the action arises independently of Miquel 

 is not yet clear. In two later experiments, each with 5 specimens, in 2 

 litres of unfiltered sterilised " outside " water only, a similar intense 

 growth was obtained. In consequence of this, it was decided to suspend 

 the use of Miquel, and using only filtered unsterilised "outside " water, 

 to reduce the number of specimens. In experiments made under these 

 latter conditions, with 1 or 2 Calanus in 2 litres of water, the growth has 

 been more often slight or moderate, though sometimes so strong, 



