90 PLANT-ANIMALS [CH. 



of the animals, we should expect that the latter, when 

 deprived of other supplies, would make larger de- 

 mands on the reserve fat of the yellow-brown cells 

 than when the animals had access to other food 

 supplies. Third, if C. paradoxa are kept in filtered 

 sea-water, and hence deprived of all food except that 

 which it can obtain from the yellow-brown cells, 

 then, so long as they are exposed to the light, the 

 yellow-brown cells continue to contain fat-globules. 

 Since animals deprived of food get just as hungry 

 in the light as in darkness, it would appear to follow 

 that the reason why the fat does not disappear from 

 the yellow-brown cells of the light-kept animals is 

 that, as fast as it is removed to serve for the nutrition 

 of the animal, it is reformed by the yellow-brown 

 cells. It is therefore to be concluded that the fat- 

 globules are reserve products of the photosynthetic 

 activity of the yellow-brown cells. 



Thus we reach a definite stage in the course 

 of our enquiry into the significance of the green 

 and yellow-brown cells of C. roscoffensis and C. 

 paradoxa. These cells are capable, in the same way 

 as the chlorophyll-containing cells of plants, of manu- 

 facturing organic, carbon-containing substances from 

 inorganic materials and of storing the surplus in the 

 form of starch or fat. 



Our next step must be to determine whether the 

 products of the photosynthetic activity of the coloured 



