180 F. KEEBLE AND F. W. GAMBLE. 



infecting organism was to have a successful termination^ to 

 begin at the other end, namely, to seek for the organism 

 before its entrance into the body of Convoluta. 



Onr observation that infection may take place, not only 

 from fresli sea-water, but also from the remnants of egg- 

 capsules laid in filtered sea-water suggested a mode whereby 

 this searcli might be prosecuted with some hope of success : 

 the mode being the isolation and observation of egg-capsules 

 from which the larvce had escaped. The isolation was neces- 

 sary because, if left with the young animals, the capsules 

 disappeared, either being torn to fine shreds by the frequent 

 entrances and exits of the larvfe or, perhaps, being devoured 

 by these larvae. Accordingly, numbers of egg - capsules 

 obtained from well-washed animals were put into filtered 

 sea-water, and as soon as the young had emerged from them 

 the ti'ansparent, gelatinous remains of the capsules were 

 removed to another vessel of filtered sea-water. There they 

 were kept under daily observation. After seventeen days 

 (Table III, columns 3 and 5) several green spherical bodies 

 of about the size of the egg-capsules made their appearance. 

 Microscopic examination showed that these spherical bodies 

 were composed each of a pure culture of vast numbers of a 

 unicellular green organism. During the examination the 

 slight pressure of the cover-glass suflficed to burst the delicate 

 membrane of the green spherule and a swarm of active, 

 flagellated cells emerged, leaving behind the recognisable 

 remains of an egg-capsule (figs. 1, 2, 3, 4, PI. 13). These 

 flagellated cells, a detailed description of which is given in 

 Section IV, presented so many features in common with the 

 green cells of Convoluta roscoffensis as to leave but 

 little doubt that they represented a free stage of these cells : 

 the cup-shaped chromatophore containing a polygonal pyrc- 

 noid, the colourless part of the protoplast occupying, as is 

 sometimes the case in the green cells of the animal, the 

 narrow cavity of the cup, the red, lateral-lying eye spot, also 

 to be met with in the green cells of recently infected young 

 Convolutas, all pointed to this conclusion. 



