242 The Animal Mind 



tained (182) that the simple eyes function with the com- 

 pound eyes to respond to changes in the depth of objects, 

 since such changes would alter the angle at which light 

 rays from the object would fall on the two sets of eyes. 

 Spiders appear to have the principal eyes adapted for 

 far visioh and the auxihary eyes for near vision, while 

 one spider, Epeira, has part of the hinder median eye 

 adapted to each (324). 



§ 70. Some Theoretical Considerations 



The temptation is strong to speculate upon the essential 

 nature of the conditions which make possible true space 

 perception, the simultaneous experiencing of sensations 

 that are referred to different points in space. Such specu- 

 lation must be of the most tentative description, yet the 

 following suggestions seem not wholly unwarranted by 

 the facts. For one thing, it looks probable that the ability 

 to suspend immediate reaction is essential to space per- 

 ception. Can a spatial complex of sensations occur in 

 the experience of an organism unless that organism is 

 capable of receiving a number of stimuli on a sensitive 

 surface and of suspending, for a brief period at least, all 

 reaction? Let us take as an example of such a complex 

 a visual field, within which different color and brightness 

 qualities are arranged in definite order, some above, some 

 below, some to the right, others to the left. Could such 

 a balance of tendencies to move the eye as is involved in 

 the simultaneous perception of a number of elements pre- 

 serving regular space relations to each other have been 

 brought about unless no single one of the tendencies were 

 irresistible? One can readily imagine an eye functioning 

 in such a way that every stimulation of it, though occa- 



