438 GEXERAL BIOLOGY 



agreeableness or disagreeableness, some sort of organic 

 sense of comfort or of discomfort, connected with and 

 occasioning the reactions of the two sorts. 



Organs of out-reach. — Impermanent pseudopodia are the 

 amoeba's only means of exploring its environment, but the 

 higher protozoans possess cilia and flagella. These are 

 permanent organs of out-reach, in which sensory and motor 

 functions are combined. These enable their possessor to 

 reach out and touch an object before coming into bodily 

 contact with it. These give time and opportunity for 

 avoidance of collisions and for escape from approaching 

 enemies. Indeed, if, with specialized sensibility, these be 

 capable of receiving vibrations, they may give warning of 

 the proximity of an enemy before coming into actual con- 

 tact with it. These make the course of an animal through 

 the water less groping in proportion to their length or 

 sensitiveness. It is the method of a blind man exploring 

 his pathway with his cane. The long fiagellum which 

 Euglena (fig. 6i on p. 105), swings before it as it swims, 

 explores a relatively wide pathway. 



But Euglena has also an "eye spot" at the forward end of 

 the body, and is capable at least of discerning between light 

 and darkness; and therefore, if compared with a blind man, 

 the comparison should be with one whose blindness is not 

 total. Euglena swims, as we have seen, habitually into the 

 better lighted areas of its watery environment. In doing 

 this it must be guided not so much by its tactile sense, 

 (which is more directly concerned with the objects of its 

 immediate environment), as by vibrations of light coming 

 from a greater distance. Here, then, is the beginning of 

 another kind of perceptive organ — one whose efficiency 

 depends, not on the out-reach of a sensitive part of the 

 body, but on specialized sensibility of a part to the inflow 

 of vibratory stimuli coming from a distance. The range of 



