ARTJFK'JAL (.'ULTUKb] OF MARINE PLANKTON ORGANISMS. 421 



In the second experiment (eggs fertilised June 8tli, 1908), 

 made with similar water, the larvas were fed a on pure culture 

 of Nitzschia closterium var., and six had completely 

 metamorphosed on July 26th (forty-eight days after fertilisa- 

 tion), two more subsequently coming through. The teinpera- 

 ture was generally 15° to 16° or 17° C. 



In the third experiment (eggs fertilised March 29th, 1909) 

 aquarium Lank-water treated with animal charcoal and then 

 filtered through a Berkefeld filter was used. Plutei fed with a 

 pure culture of a snuill flagellate (probably Chilomouas sp.) 

 grew satisfactorily, and eight young Echinus were found on 

 June 5tli (sixty-eight days after fertilisation), which had 

 probably metamorphosed some days earlier. Two other jars, 

 in which Nitzschia closterium var. was used as food, 

 were not successful, pi-obably because the growth of diatoms 

 became too tliick towjirds the end of the experiment. 



Echinus mi liar is. — In the first experiment with this 

 species animal-charcoal Berkefeld water was used, each jar 

 containing, as usual, 2000 c.c. In one jar the Plutei, from eggs 

 fertilised on August 27th, 1907, were fed on a pure culture of 

 Nitzschia closterium, var. On October 4th, i.e. thirty- 

 eight days after fertilisation, one Echinus has just metamor- 

 phosed. On October 29th about a dozen healthy-looking 

 Echini were climbing about the jar, and many were still in 

 a healthy condition on January 8th, 1908. Temperatures : 

 September, 15° to 19° C. ; October, 16° dropping to 13° C. 

 towards end; November, 12° to 11° C; December, 15° 

 to 10° C. 



To another jar coutaining larvae from the same batch a few 

 drops of fresh Plankton were added as food. The Plutei in 

 this case fed on flagellates and Nitzschia which grew in the 

 jar, and several metamorphosed. 



In a second experiment with eggs fertilised on September 

 13th, 1907, the larvae were fed with Nitzschia closterium, 

 but although there were a few well -advanced plutei still 

 living on January 8th, 1908, none completed the meta- 

 morphosis. 



