ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 465 



back clusters of eggs or other large material. The filtrate is divided 

 amongst a number of tall narrow beakers containing sterile sea- 

 water, and the beakers, after being covered with a glass plate, are 

 placed where the temperature will be uniform and not rise much 

 above 15° C. In the course of twenty-four hours the healthy larvie 

 will swim up to the surface and can be easily seen and removed from 

 vessels of this shape. They are transferred by means of sterile pipettes 

 to jars* of sterile sea-water, about fifty to seventy larvtf being put in 

 each jar of 2000 c.c. sea-water. At the same time, a good pipetteful of 

 a pure culture of diatom is added to each jar. The small diatom 

 Nitzschia closicrium, forma minutissima, we have found most useful, as 

 its size is suitable, and it grows well in animal-charcoal tank-water, 

 floating throughout the body of the water, and so being in intimate ad- 

 mixture with the larvcT. The jars are placed in a moderate light and at as 

 even a temperature as possible.f No further attention is necessary until 

 the larvie have metamorphosed. The metamorphosis takes place in from 

 six to nine weeks after fertilization. Larvte may be taken out from 

 time to time and examined to see if they are feeding well. If the 

 diatoms do not grow sufficiently rapidly in the jar, more should Ije 

 added from the culture flasks. We are more often troubled, however, 

 towards the end of an experiment Ijy an excessive abundance of 

 diatoms. In this case the jar may either be put in a darker place or 

 some of the water may be drawn off and replaced by a fresh supply of 

 sterile sea-water. Care should be taken to have a sufficient supply of 

 food at the beginning of the experiment, so that the larvte may be 

 able to feed as soon as they are ready for food. 



The method just described can be modified in various ways without 

 detriment to the result.- Sufficient sterilization of the water may be 

 effected by heating to 70° C. for fifteen minutes, after which it should 

 be aerated by violent shaking ; " outside " water may be used instead 

 of " tank-water," and may be treated with Miquel's solutions in the 

 ordinary way, to ensure a satisfactory growth of the food-diatom. 



With regard to the food organisms, we have tried to obtain as large 

 a variety of these in pure culture as possible, and then to make trial 

 of a number of them with each batch of larvte on which we have 

 experimented. If no suitable pure cultures are available, success can 

 sometimes be obtained by adding a few drops of tow-netting, collected 

 with a fine-meshed net (180 meshes per inch), directly to the treated 



* Tlie vessels we use are ordinary green glass sweet-jars, having a capacity of about 

 2000 CO., whicli are kept covered witli the glass stoppers provided with such jars, from 

 which the cork band has been removed. 



t In liot weather we often stand the jars in one of the tanks of circulating aquarium 

 water, wliich maintains them at a very uniform temperature. 



