276 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



Culture dishes are prepared by taking sci'apings from the laboratory tanks, and 

 allowing them to grow in the dishes in the modification of Miquel's culture solution 

 described by Allen and Nelson (3). By this means, at the end of a fortnight 

 a thick growth of various Algae and Protozoa becomes established in the dishes. 

 The Miquel solution is then poured off from the latter, and they are filled up with 

 sea-water, taken, as before, at a considerable distance from the shore. In these 

 dishes are placed the young Echini, and on this food they increase rapidly in size. 

 The water in the dishes is changed about once a week. The best food-stuff" seems to 

 be the calcai'eous protozoan Trichosphmrium, which probably furnishes some of the 

 large amount of the calcareous matter necessary for the building up of the test and 

 spines of the Echini. When the latter have reached a size of over 2 cm. across the 

 spines, they flourish on another calcareous food, namely the red alga Corallina. 



Briefly to compare, therefore, the conditions under which the larvae were kept in 

 the laboratory, with the conditions under which they would naturally develop 

 In the sea, these are as follows : — 



1. The conditions imposed by their fertilization In an artificial manner and the 

 possible immaturity of the germ cells. 



2. The filtered water in which the animals are grown is different to some extent 

 chemically from normal sea-water. The changes taking place by filtering are such as 

 to render it always of low alkalinity, Ph = 7"40, as compared with P,, -- 8 of normal 

 "outside" water. Certainly, many of the puti'efactive elements are eliminated, 

 while the organic matter is removed by filtration through porcelain. In any case, it 

 is safe to assume that the " Beikefeld " water differs considerably from ordinary 

 sea-water. This point has been gone into ])y Allen and Nelson (3). 



3. The temperature of the culture jars varied from 10° to 16° C. The sea 

 temperature is always much below this, oidy rarely in the hot summer months 

 reaching 16° over the sandy patches near the shore. 



4. The larvge had only one kind of food, i.e., Nitzschia closterium. 



5. The water in which they lived was always still and never in movement. 



To avoid some of these abnormal laboratory conditions, we constructed, in the season 

 of 1911, a sunk raft with submerged chambers, in which we could place numerous 

 jars containing plutei. During the seasons of 1911 and 1912 this raft was anchored 

 out In the clear water of Cawsand Bay, several miles from the contaminated and 

 more or less completely land-locked waters of the inner portion of Plymouth Sound. 

 This was the most suitable situation we could find, as the strong winds and rough 

 tidal waters of the Channel made it quite impossible to place it in the open sea. 

 In the region of the Echinus beds. It was necessary to place it to some extent 

 mider the shelter of the land, to pi^event its being washed away during storms, 

 and at the same time to allow of its being visited several times a week, even during 

 bad weather. 



