Echinoderm LarvcB with Two Water- Vascular Systems. 335 



10 or 11 days in the hypertonic water, the hydrocoele was formed on the 

 left side as in normal cultures, but in some larvce there appeared on the right 

 side an outgrowth from the right anterior ccelom in the form of a little vesicle, 

 lahich ivas not present in normal larvce {r.hy., fig. 3). I hailed this structure 

 as a rudiment of a right hydroccele, but no amniotic invagination was formed 

 over it, and, in spite of all my endeavours, the larvae refused to develop 

 further, and so this experiment led to an indecisive result. 



In 1915 the experiment was repeated, and the same result was obtained. 

 Some of the most promising larvae were picked out and placed each in 

 normal sea-water in a separate finger-bowl, with a rich supply of Nitzschia. 

 In one of these larvae the bud on the right side developed five lobes, showing 

 that it really was a right hydroccjele ; the other specimens died. 



In 1916 the experiments wove again repeated, and, during that year, some 

 larvae were kept living in Breflit jars filled with the hypertonic water, 

 whilst others, after having been for periods varying from a week to three 

 weeks in this water, were transferred to Breftit jars filled with normal 

 sea- water. At the end of six weeks I had the immeasurable satisfaction of 

 seeing some larvae belonging to both categories develop an unmistakable 

 right hydrocoele, provided with five tentacles, which projected into a 

 well-formed amniotic cavity (fig. 7). In these experiments, the tendency 

 of the hypertonic water to inhibit the growth of the Nitzschia was overcome 

 by the constant addition of fresh doses of Nitzchia. 



I was still, however, far from satisfied with the results which I had 

 obtained. The larvae grown in the Breffit jars v/ere in some respects 

 unhealthy, as fig. 7 shows, and the number which survived until reaching 

 the stage when the hydrocoele develops lobes was small, and so I made 

 arrangements to repeat the experiment on a large scale during the summer 

 of 1917. 



Owing to difficulties connected with the war, I was unable to secure a 

 supply of sea-urchins until July 7. The experiment was closed on 

 August 14, and so it lasted only between five and six weeks — an insufficient 

 amount of time to allow of the larvae completing their metamorphoses, but 

 long enough to allow of them producing large Echinus-rudiments with all 

 their characteristic features. As I have already mentioned, the urchins sent 

 me in this year (1917) were collected at Looe Island, and I have reason to 

 believe that, owing to the experience of the assistants of the Plymouth 

 Laboratory, who packed and forwarded them, they reached me in better 

 condition than the urchins which I received in 1915 and 1916. 



I decided to increase the salinity of the water, not by evaporation, but by 

 the addition of 5 grm. of common salt to each Breffit jar, which raised the 



