Eyea of Molhiscs and Arthropods. 713 



accumulateci in this mauner,it is suddenly discharged, in large or small 

 quantities. in the shape ofmotiou. In all except the veiy lowest animals , 

 the energy liberated as motion more thau equals that absorbed directly 

 from the light; for this motion is the sum of the energy absorbed by 

 the animai from the sun, and that which was absorbed by plants 

 in the production of suitable food for the animai. We can say that 

 vegetable protoplasm times sun energy and inorganic matter, to the 

 n*^ power, equals x organic matter. Animai protoplasm times orgauic 

 matter and energy, to the n*^ power, equals motion and inorganic matter. 



Plauts Store energy; animals convert it into motion. 



Heliophags, or sun consumers, are found in animals as well as 

 plants. In the latter instance, they are usually present as Chlorophyll 

 granules, whieh, in some zoospores of the lower plants, are spe- 

 cially moditied to form red pigment spots, usually situated near the 

 ciliated pole of the spore. They probably represent modifications of 

 Chlorophyll adapted for the consumption of especially large quantities 

 of sun energy. Such spores are extremely active and heliotropic. In 

 Protozoa. we also find special modifications of the pigment, or of the 

 Chlorophyll, to form »red eye spots«. They likewise have a tendency to 

 be formed at the animai pole, where the vital processes are presumably 

 most active. In the Coelenterates and Echinoderms , we have pigment 

 spots which, without doubt, are homologous with, and have the same 

 functions, whatever they may be, as those seen in Protozoa, and in the 

 zoospores of certain plants. The pigment, always red but occasioually 

 containing black, is here deposited in special cells in such a manner, 

 however, that their relation with the simpler eyes of the Mollusca and 

 Worms is placed beyond doubt. 



Now we have already come to the conclusion that pigment and 

 Chlorophyll are different phases of the same substance, and have essen- 

 tially the same function, i. e. absorption of the chemical rays, or of the 

 energy of the sun. But we can show, by a comparison of the lowest 

 forms of ocelli , such as those formed in Protozoa , Coelenterates and 

 Echinoderms , with those of still higher forms , that the ocelli are the 

 bodies of ali others which stand in most intimate and dependent rela- 

 tion with the sunlight; but they are especially eharacterised by the 

 high form of pigment that they contain ; therefore we are led to suppose 

 that the red and black pigment, but principally the former, have in the 

 highest degree the power of absorbing energy from sunlight. If this 

 be true, then the accumulations ofp ig ment cells, called ocelli, 

 are organs especially adapted for the absorption of sun 



