34 Colouration in Animals and Plants. 



of the lowest forms of life, which are almost mere specks of proto- 

 plasm, are influenced by light, some seeking and others shunning it. 

 He found, too, that in the case of Euglena viridis it would seek the 

 light only if it " were allowed to fall upon the anterior part of the 

 body. Here there is a pigment spot ; but careful experiment showed 

 that this was not the point most sensitive to light, a colourless and 

 transparent area of protoplasm lying in front of it being found to be 

 so." Commenting upon this Romanes observes, " it is doubtful 

 whether this pigment spot is or is not to be regarded as an exceed- 

 ingly primitive organ of special sense." Haeckel has also made 

 observations upon those lowest forms of life, which, being simply 

 protoplasm without the slightest trace of organization, not even 

 possessing a nucleus, form his division Protista, occupying the no- 

 man's-land between the animal and vegetable kingdoms. He finds 

 that " already among the microscopic Protista there are some that 

 love light, and some that love darkness rather than light. Many 

 seem also to have smell and taste, for they select their food with 

 great care. . . . Here, also, we are met by the weighty fact that 

 sense-function is possible without sense organs, without nerves. In 

 place of these, sensitiveness is resident in that wondrous, structure- 

 less, albuminous substance, which, under the name of protoplasm, or 

 organic formative material, is known as the general and essential 

 basis of all the phenomena of life."* 



Now, whether Romanes be correct in doubting whether the 

 pigment-spot in Euglena is a sense organ or not, matters little to 

 our present enquiry, but it certainly does seem that the spot, ivith 

 its accompanying clear space, looks like such an organ. And when 

 we are further told that after careful experiment it is found that 

 Euglena viridis prefers blue to all the colours of the spectrum, the 

 fundamental fact seems to be established that even as low down as 

 this the different parts of the spectrum affect differently the body of 

 creatures very nearly at the bottom of the animal scale. This 

 implies a certain selection of colour, and, equally, an abstention from 

 other colours. 



It is not part of our scheme, however, to follow out in detail the 

 development of the organs of special sense, and the reader must be 

 referred to the various works of Mr. Romanes, who has worked long 

 and successfully at this and kindred problems. Suffice it to say that 

 in this and other cases he has been led to adopt the theory of 

 * Quoted by Romanes, op. cit. p. 81. 



