86 THEORETICAL BIOLOGY 



of the subject, we should not speak of an appearance-world, but 

 only of a surrounding-world built up from our own qualities. 

 Since knowledge of the other subject's " mark-signs " is denied 

 us also, we are confined to determining what properties of our 

 appearance-world have value as " indications " in the sur- 

 rounding-world of an animal. These indications (which must 

 become mark-signs for us, if we are to experience anything of 

 them at aU), we shall treat like our own qualities, so far as 

 possible, and arrange them in the forms given us a priori. 



We see a justification for this proceeding in the fact that 

 the anatomical structure of the sense-organs of animals brings 

 together as a unity those indications that our attention also 

 treats as a unified quality-circle. 



Nevertheless, we should never forget that, so long as we 

 are concerned with biology, we must not for an instant desert 

 our posts as observers from the outside. 



