466 ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



sterile water coiitaiiiinL;- tl>e larva:'. In this case one depends on the 

 chance of a suitable food organism growing in the vessel unaccom- 

 panied by any destructive organism. On several occasions a satis- 

 factory result has been reached ])y proceeding in this wa}^ and tlie 

 method is generally worth a trial, seeing that the number of larvaj 

 obtainable from an ordinary fertilization is veiy large, and many 

 different experiments are easily made with them. 



AVe will now give details of some of the results obtained by making 

 use of the methods described, or of their modifications. 



Echinus acittus. — The first successful experiment was made with 

 this species. Eggs fertilized on June 13th, 1905, produced healthy 

 larvae, 50 to 75 of which were placed, three days later, in a glass 

 jar containing 2000 c.c. of outside sea-water, filtered through animal 

 charcoal, to wdiich modified Miquel solutions were added. They were 

 fed on a diatom culture, containing a small species of Chaetoceras, wliicli 

 did not form chains, a small diatom probably belonging to the genus 

 Mdodra, a small Naviculoid diatom, two minute flagellates, and a 

 small green organism, probably one of the Pleurococcacccc. The vessel 

 stood in a shallow tank, through which a stream of aquarium water 

 was flowing, and the temperature was fairly constant at 15° or 16^ C, 

 though there is one record of 19° C. at the end of July. The first 

 two young Echinus were seen on July 25th, 42 days after fertilization, 

 and on August 1st 20 were counted. On August 5th (the 53rd day) 

 a careful search through the jar gave 21 young Ecliinus of normal size 

 attached to the glass, 6 minute but fully formed Echinvs, about 23 

 still in the Pluteus stage, roughly lialf of which were well advanced. 

 On August 16th some of the water, which had not been changed since 

 the beginning of the experiment, was replaced by " outside " water. 

 On October 5th (16 weeks after fertilization) 12 Echinus were still 

 alive. Some pieces of red seaweed were placed in the jar, upon which 

 the Ecliinus fixed themselves and fed. Several of these specimens 

 lived for over a year, but sufficient attention was not given to finding 

 suitable food for them after the metamorphosis, so that they did not 

 grow very large. 



Ecliinus csculentus. — Three successful experiments have been made 

 with E. csculentus. In the first (eggs fertilized April 5th, 1907) "out- 

 side " water treated with animal charcoal and filtered through filter- 

 cloth, but not otherwise sterilized, was used. A number of jars of 

 2000 c.c. capacity containing larva? were set up, and, to the most of 

 these, various diatom cultures then in our possession were added, none 

 of which, however, gave a satisfactory result. In two jars, on the 



