8o MIND IN EVOLUTION CHAP. 



plasticity is partly a matter of degree, partly of the pro- 

 cesses at the disposal of the instinct. At one end of the 

 scale we have mechanical sequences approximating to the 

 reflex type. Moving upwards from these we have 

 adaptations, at first slight and afterwards important. 

 The simplest of these may be explained as sensori- 

 motor acts, where the instinctive interest determines the 

 manner in which sense data are combined so as to yield 

 an appropriate response, but, still within the sphere of 

 instinct, we reach a point where the new combinations 

 effected in surmounting obstacles or in dealing with 

 difficult situations must be referred to intelligence. The 

 criteria of intelligence will be dealt with separately. We 

 cannot in all cases decide with certainty whether it is a 

 factor, but it is impossible to deal with the higher instincts 

 at all without admitting its possibility. 



Whether intelligence is present in the following case must 

 be left to the judgment of the reader, but it will suffice to 

 illustrate the manner in which actions are combined and 

 adjusted under the instinctive interest. A sandhopper is 

 feeding amongst seaweed and a crab 1 approaches behind a 

 clump of weed, which he uses as " cover." There was a 

 distance of about eight inches between the two animals, 

 which the crab had to cross without alarming his victim. 

 Presently he left his cover, and, crouching down, crept 

 towards the sandhopper. When he had got about half 

 way, the sandhopper stopped eating, and turned towards 

 the crab, which immediately disappeared in the sand. 

 Presently the sand rose nearer the sandhopper, the 

 crab reappeared, took a stealthy step or two towards 

 the victim, and then sprang upon him. There are 

 here a succession of acts of diverse character- 

 watching, stealthy creeping, hiding, and pouncing, all 

 brought into operation as the case requires. The whole 

 series turns upon a fixed point the seizure of the prey ; 

 and each of the varied set of acts is adopted in accordance 

 with the varying actions of the prey, or the varying re- 

 lations between it and the hunter. If we try to regard 



1 Dr. Oscar Schmidt in Brehm's Thierleben, as quoted by Schneider, 

 p. 324- 



