388 F. W. GAMBLE AND FUEDEEICK KEEBLE. 



capsule was possible. Bright liglit^ diffuse light, and dark- 

 ness were employed. No sand was introduced, as we found 

 that the reserves afforded quite sufficient nourishment to 

 enable the Convoluta to live and develop for a couple of 

 weeks. 



The experiment was begun on September 9th, and lasted 

 till September 21st. The results showed the value of the 

 precautions. Those cultures which had been made by sub- 

 jecting isolated embryos or larvte to filtered water showed 

 no trace of colourless cells, although several dozens of such 

 isolated specimens were employed. The cultures in water 

 sterilised at 60° C. and at 80° C. showed but three cases 

 of colourless cells in between thirty and forty larvje, all of 

 which had grown and developed and Avere active at the time 

 of closing the experiment. Sterilised cultures in which the 

 egg"-capsule had been inserted showed a much higher per- 

 centage of the occurrence of colourless cells. In ordinary 

 sea-water cultures, both with or without capsules, colourless 

 cells were almost invariably present. I^hese results point 

 very decidedly to the capsule or sea water as the source of 

 the colourless cells. 



3a. Conclusions on the Origin of the Green Cells. 



We may now sura up the evidence we have obtained as to 

 the origin of the green cells of Convoluta. There is no 

 habitual infection of Convoluta by a green cell. The 

 future assimilating tissue consists at first of colourless cells. 

 No trace of either green or colourless cells or of plastids has 

 been found before the time of hatching. 



The evidence gained by isolating embryos and larva; in 

 sterilised and filtered water goes to show that the more care 

 is exercised in preventing contamination from the capsule, 

 the fewer ciises of colourless cells are subsequently registered. 

 Access to the capsule and the use of ordinary sea water 

 favour the appearance of colourless cells. It is therefore 

 probable that the colourless cells iulcct the larval Convoluta 



