222 Phylum Art hr op oda 



ber of which could be set in a large crystallizing dish and covered with a 

 glass plate, were found especially convenient and were suitable for two 

 copepods each. 



Water. The water used in the containers was ordinarily taken from 

 the laboratory salt water tap. No improvement was found to result 

 from using water brought in directly from the harbor or from Vineyard 

 Sound. In a few cases the copepods appeared to fare perfectly well for 

 a week or two without any change of water. In other cases the copepods 

 were transferred after a certain number of days by means of a pipette 

 to fresh containers, but this procedure was very laborious and often re- 

 sulted in the loss or injury of some of the animals. A better method was 

 to pour away all but a little of the original culture medium, leaving the 

 copepods in the bottom corner of the dish and then to replenish with 

 fresh seawater. It has not yet been determined how frequently it is 

 necessary to change the culture water under various conditions. Very 

 good survival was obtained in two sets of experiments, described in detail 

 by Clarke and Gellis (1935), in which the culture medium was run 

 continuously through flasks in which the copepods were confined. 



Stirring and Aeration. If the copepods were at all crowded they died 

 off rapidly unless stirring in some form was provided. When beakers, 

 or other wide-mouthed vessels, are employed, stirring may be accom- 

 plished conveniently by using glass plungers activated by the Plymouth 

 siphon device [Harvey, 1928, p. 57] or by an electric motor (Hagmeier, 

 1930) . Such stirring provides at the same time a certain amount of aera- 

 tion, which is probably sufficient in most cases. More effective aeration 

 may be obtained by bubbling compressed air from a tap filter pump slowly 

 through the water by means of glass tubes reaching to the bottom of the 

 containers. The stream of bubbles brings about a slow circulation of 

 the water which makes mechanical stirring unnecessary. This method 

 is especially convenient for narrow-mouthed containers such as Erlen- 

 meyer flasks. When small culture dishes were used with only a few 

 copepods in each, stirring and aeration were found unnecessary. 



Temperature. Temperature was controlled by placing the Erlenmeyer 

 flasks and the crystallizing dishes in a constant temperature tank where 

 they rested half submerged on a wire rack. Two of these tanks were 

 available and were maintained at different temperatures (kept constant 

 to o.i° C.) by means of two Kelvinator cooling units operated by 

 Hiergesell thermo-regulators and relays. A third and lower temperature 

 (5-6 C.) was obtained by placing the containers in a large refrigerator. 

 It was found that for all the species investigated the copepods died off 

 rapidly if the temperature was allowed to rise above 20 C. Below 20 C. 

 in the case of Calanus survival was improved progressively at lower 

 temperatures down to 5-6 C, but the molting of shells became less 



