v] NATURE OF PL ANT- ANIMALS 149 



Let us appeal therefore to C. paradoxa. A far more 

 greedy feeder than the green species, its accumula- 

 tions of nitrogenous waste substances are much larger 

 than are those of its ally. Inspection of the Frontispiece 

 or of Fig. 4 shows well-marked, granular bands across 

 the body of the animal. These bands consist prob- 

 ably, as von Graff has suggested, of urates. They 

 are slight in the young animal, increase as it matures, 

 but may disappear as the period of egg-laying arrives, 

 at which time the yellow-brown cells have developed 

 to their full extent. 



In order to establish our hypothesis we must 

 demonstrate that the yellow-brown cells of C. para- 

 doxa actually make use of such substances pre- 

 sumably uric acid or urates as are stored in the 

 body. 



For this purpose, two modes of experimentation 

 were adopted. In the first method, batches of animals 

 of similar sizes and origin were maintained in the 

 light in filtered sea-Avater to which uric acid was 

 added and their condition was compared with that 

 of animals kept in filtered sea-water containing no 

 uric acid. Preliminary observations showed that the 



V 



uric acid added to the sea- water was taken up readily 

 by the animals and stored in vacuoles in the tissue 

 of the digestive tract. Examination and measurement 

 of animals from the two batches those in filtered 

 sen- water only and in filtered sea- water plus uric 



