174 p. KEEBLE AND F. W. GAMBLE. 



In our previous work (1903), where strong, but not decisive, 

 evidence in favour of tlie infection-hypotliesis was given, we 

 showed that it was possible to maintain young Convoluta 

 alive and colourless for several weeks. The freshly laid egg- 

 capsules containing the groups of fertilised eggs were — in 

 these experiments — removed from the neighbourhood of 

 adult animals and placed in sea-water which had been filtered 

 by means of a Pasteur-Chamberland filter. Tlie animals 

 hatched out in the course of two or three days as colour- 

 less larvae and remained colourless for two or even three weeks 

 (Table II, Columns A and D). Samples of these colourless 

 animals taken at any time during this period and placed in 

 fresh, unfiltered sea-water became green in three or four days. 



So far the result of this experiment pointed most definitely 

 to the environment as the source of the gi-een cells ; but this 

 conclusion was rendered less certain by the subsequent 

 behaviour of the animals reared in filtered sea-water. Certain 

 among these, sometimes few, sometimes many, ultimately 

 became green, and ou microscopic examination were found 

 to be possessed of normal green cells (Table II, Columns B 

 and C). The sporadic and tardy appearance of green indi- 

 viduals among the Convoluta hatched in filtered sea-water 

 could be accounted for best on the supposition that small 

 numbers of the infecting organism had been introduced with 

 the egg-capsules into the filtered water, and that the three 

 or four weeks which elapsed before infection took place were 

 required for the multiplication of this organism. Microscopic 

 examination of the egg-capsules showed the high probability 

 of this supposition, for tliey were found to be infested, even 

 a day or so after they had been laid, and before the young 

 had escaped from them, with numberless green and colourless 

 cells of various kinds. 



To eliminate this source of error it was necessary therefore 

 to obtain capsules as clean as possible, and to take the pre- 

 caution of isolating the young from this source of infection. 

 This we succeeded in doing by the following somewhat 

 laborious process. 



