CHLOEOPHYLL IN ANIMALS. 71 



chlorophyll ; thus in these exceptional cases the influence of 

 light appears to be almost or entirely excluded. We venture 

 to assert that this contrast holds good in by far the larger 

 numbor of animals and plants, and it is quite certain that 

 true eyes are never found in plants, while it still remains doubt- 

 ful whether chlorophyll doss actually occur, as has often been 

 asserted, even in the lowest animals. Theoretically its existence 

 in animals is certainly not impossible; and this theoretical 

 possibility has perhaps given rise to the assertion. The wide 

 interest which attaches to this assumption may justify us in 

 digressing here into a somewhat closer discussion of the data 

 relating to the matter. 



The chlorophyll bodies of plants are, as is well known, 

 microscopic and elementary bodies of peculiar structure and of 

 definite function ; their principal property is that they decom- 

 pose carbonic acid under the influence of light, and form organic 

 compounds by the combination of three or four elements. 

 This true chlorophyll has, besides, properties which allow the 

 botanist to distinguish, when necessary, whether the green 

 colour of a newly discoA'ered plant is actually caused by the 

 presence of chlorophyll, without any need of previously investi- 

 gating whether the green particles decompose and assimilate 

 carbonic acid. Among these properties are certain absorption- 

 bands in the spectrum of solutions of chlorophyll, its direct 

 dependence on the presence or absence of light, its reaction 

 under certain chemical agents, and its peculiar microscopic 

 structure. In most cases it is suifioient for the botanist to have 

 detected any one of these features when the case in point is to 

 prove whether the green colour of a plant depends on chloro- 

 phyll. Besides thi^, so far as I know, no exception worth 

 mentioning has hitherto been admitted to the rule, that the 

 green colour of all plants is occasioned not by any true pigment, 

 but by the presence of chlorophyll. In animals, however, the 

 case is quite different. We know that most animals are 

 absolutely incapable of decomposing carbonic acid ; but they 

 are, nevertheless, frequently of a green colour. In by far the 

 greiiter number of cases this green colour is undoubtedly due 

 not to chlorophyll, but to a true pigment. Hence we cannot 



