420 K. .). ALI.KN AND K. W. NliLSOX. 



minute flagellntes, uiid a siiuill gi-euu oi-ganism, probably one 

 of the Pleurococcaceae. The vessel stood in a shallow 

 tank, through which a stream of aquarium water was flowing 

 a-nd 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- Echiii us were seen on July 25th, forty-two 

 days after fertilisation, and on August 1st twenty were 

 counted. On August 5th (the fifty-third day) a careful 

 search through the jar gave twenty-one young Echinus of 

 normal size attached to the glass, six minute but fully formed 

 Echinus, about twenty-three still in the Pluteus stage, 

 roughly half of which were well advanced. On August 10th 

 some of the water, which had not been changed since the 

 beginning of the experiment, was replaced by " outside " 

 water. On October 5th (sixteen weeks after fertilisation) 

 twelve Echinus were still alive. Some pieces of red seaweed 

 were placed in the jar, upon which the Echinus fixed them- 

 selves 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. 



Echinus esculentus. — Three successful experiments 

 have been made with E. esculentus. In the first (eggs 

 fertilised April 5th, 1907), "outside" water treated with 

 animal charcoal and filtered through filter-cloth, but not 

 otherwise sterilised, was used. A number of jars of 2000 c.c. 

 capacity containing larva3 were set up, and, to the most of 

 these, various diatom cultures then in our possession were 

 added, none of which, however, gave a satisfactoiy result. 

 In two jars, on the other hand, to which no culture was 

 added, there was considerable growth of diatoms and of a 

 flagellate, upon which the Plutei fed. The first young 

 Echinus were recorded in both jars on June 8th (sixty-four 

 days),, but may have been present a few days earlier, 

 l^ventually from thirty to forty metamorphosed in one jar 

 and about twelve in the other. The temperature varied from 

 10-5° C. to 12-5° C. 



