AKTIFK'IAL CULTURE OF MAlUNK PLANKTON ORGANISMS. 419 



be taken to have a sufficient supply of food at tlie beginning 

 of the experiment, so that the larvae 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 sterilisation 

 of the water may be effected by heating to 70° C. for 

 fifteen minutes, after which it should be aerated by violent 

 shaking. "Outside Avater" 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 

 larvae 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 

 sterile water containing the larvas. In this case one depends 

 on the chance of a suitable food-organism growing in the 

 vessel, unaccompanied by any destructive organism. On 

 several occasions a satisfactory result has been reached by 

 proceeding in this way, and the method is generally worth a 

 trial, seeing that the number of larvae obtainable from an 

 ordinary fertilisation is very large and many different 

 experiments are easily made with them. 



We will now give details of some of the results obtained by 

 making use of the methods described, or of their modifications. 



Echinus acutus. — The first successful experiment was 

 made with this species. Eggs fertilised on June 13th, 1905, 

 produced healthy larv^, fifty to seventy-five of which were 

 placed, three days later, in a glass jar containing 2000 c.c. of 

 ouside sea-water, filtered through animal charcoal, to which 

 modified Miquel solutions were added. They were fed on a 

 diatom culture, containing a small species of Cheetoceras, 

 which did not form chains, a small diatom probably belonging 

 to the genus Melosira, a small naviculoid diatom, two 



