EXPERIMENTS IN THE KEEPING OF PLANKTON ANIMALS. 567 



was in the former case 43 days, and in the latter 17 days when the last 

 record was made. It is only noticeable that in Position C the fertility 

 of the parents was distinctly higher than in Position A. It seems 

 probable that the species is hardy as compared with others and less 

 susceptible to injury from changeable conditions (cf. p. 561). 

 For Calanus, the comparative results are as follows : — 



Position A. 



(1) Finger-bowls. Mcik. for o experiments (34 specimens), 40 days. Avg. 12 days. 



(2) l-litre flasks. „ 5 „ (19 „ ), 84 „ „ 22 „ 

 (;j) Special expt. „ 1 „ ( 5 „ ), 28 „ „ 21 „ 



Average for 11 experiments, 17 „ 



Position C. 



(1) 2-litre beakers. Max. for 2 completed exps. (7 specimens), 48 days. Avg. 27 days. 



Of 3 uncompleted experiments, one with 3 specimens showed at the time of 

 the last record an average of 41 days ; the other two, with 8 specimens, 

 showed on the 45th day an average of 40 days. 

 The average for these 5 experiments then exceeded 35 days. 



(2) 1 -litre flasks. The 4 experiments (12 specimens) were very incomplete at the 



time of their interruption, only one death having occurred in each of two 

 of them, on the 16th and 30th days respectively, or over a period averaging 

 in the 4 experiments not less than 20 (or 23) days. 



The 5th flask experiment is omitted from consideration here. The 

 Bacteria by which the water became infected appear to be comparatively 

 uncommon, and, if the general form of the strands produced by them can 

 be relied on as characteristic, they were only twice observed, each time 

 with fatal results to the animals. 



Disregarding the last experiment, it may reasonably be estimated that 

 the average for the 4 experiments with Calanus in 1-litre flasks would 

 not have been less than that shown by the 5 others in Position C at the 

 close of the observations, viz., 35 days. 



In regard to experiments in Positions A and B generally, the early 

 falling off of specimens is noticeable in nearly all the results, thus : — 



For Temora, the average of 9 experiments in finger-bowls was not 

 more than about 5 days ; that of 2 experiments in 1-litre flasks was about 

 the same ; in 2 experiments in 11-litre bell- jars, few survived the first 

 fortnight. 



With Anomalocera, the 2 experiments with 9 specimens in finger-bowls 

 showed an average of 2 days only, with a maximum of 4 days. 



With Nauplii, especially those of Balanus, Temora, and Calanus, 

 introduced direct from the townettings into finger-bowls, the mortality 



