380 F. W. GAMBLE AND FREDERICK KEEBLE. 



succeeded in obtaining cultui'es of tlie algte from the green 

 corpuscles of Hydra viridis, and has taken precautions to 

 prevent the infection of these cultures by alga3 f rom without. 



In this paper the first form of chlorophyll alone concerns 

 us, and Ave may briefly consider the evidence for the algal 

 nature of green and yellow cells, and the part they are 

 supposed to play in the animal's economy. The evidence for 

 their algal nature is of threekinds — histological, physiological, 

 and developmental. As regards structure, Brandt and others 

 have shown that many yellow cells and some green ones 

 possess characteristic algal features : an eccentric nucleus ; 

 a cellulose wall; a chromatophore, containing chlorophyll and 

 fi'equently a superficial brown or red pigment; a pyrenoid ; 

 an eye-spot (Zooxanthella conductrix, Famintzin, 1891), 

 starch, and other inclusions; a biciliate swarm-spore stage (in 

 Collozoum, Brandt, 1883). The physiological evidence is 

 afforded by the work of Geddes, Brandt, and others. These 

 authors have shown that the chlorophyll of these green and 

 yellow cells photosynthesises carbohydrate in the presence of 

 light with concomitant evolution of oxygen, and that the 

 surplus assimilate is stored as starch. Lastly, the develop- 

 mental evidence which is due to Brandt (1883) showed that 

 certain anemones infested by brown cells discharged these 

 cells if placed in darkness. He then put such depleted speci- 

 mens in filtered and in unfiltered sea water, and showed that 

 the brown cells did not develop in the former, but appeared 

 in a few hours in the latter. Evidence of a slightly different 

 kind has been adduced for the green cells of Hydra, of Para- 

 m e c i u m, and of S te n to r, by Beyerinck (1890, p. 745, Note 1, 

 and p. 784) and Famintzin (1889, 1891) respectively. These 

 authors made cultures of the cells in various media, and 

 obtained stages identical with those of the common fresh- 

 water al ga, C h 1 o r e 1 1 a vulgaris. 



The proof of the algal nature of these zoochlorclliB and 

 zooxanthella; is fairly complete. The part they play in the 

 animal economy is, however, far from clear. The most widely 

 accepted hypothesis is the one associated with the term 



