iv] GREEN CELLS OF CONVOLUTA 115 



The discovery that the green cells of C. roscoffensis 

 arise, in the larval animal, from a colourless cell 

 which lies in a vacuole near the mouth of the animal, 

 makes it all but certain that they are of extraneous 

 origin, and that, in the course of ingesting solid food, 

 the larvae take up also these antecedents of the green 

 cells. 



Failing the isolation and cultivation of the green 

 cells, and failing the discovery of the colourless 

 or green cells in the sea-water, all that seemed pos- 

 sible to do more was to demonstrate that animals 

 hatched in pure, filtered sea-water, remain colour- 

 less. The method adopted for this purpose was as 

 follows. Large numbers of animals were scooped up 

 in a watch-glass as free from sand as possible. They 

 were brought into the laboratory, allowed to geotrope 

 into a white cup and washed repeatedly with filtered 

 sea-water. Their habit of sticking to the surface of 

 the cup after it had been tapped gently, permitted 

 of the water being poured off without any consider- 

 able loss of animals. After washing them many 

 times, the animals were transferred to filtered sea- 

 water in large glass dishes. In due season, the egg- 

 capsules were formed and since, though very minute, 

 they are visible readily to the practised eye, they 

 could be picked out and transferred yet again to 

 filtered sea-water. In this they were allowed to 

 hatch. Though the results of such experiments, 



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