THE INSTINCTS OF ANIMALS 149 



This remarkable instinct is associated with a structural peculiarity, 

 for without the arborescent tentacles the fishing would not be nearly 

 so successful. Other sea-cucumbers or Holothurians have different 

 tentacles, and use them in quite a different manner, filling the mouth 

 with mud by means of them. 



Very frequently, indeed, there are visible structural changes 

 associated with the modified food-instinct. Most predatory fishes 

 chase their prey, like the pike, the perch, and the shark, but there are 

 also lurkers, and these show in addition to the lurking instinct certain 

 definite bodily adaptations, without which this instinct could not have 

 such full play. 



Thus in a marine fish known as the ' star-gazer ' ( Uranoscopus) 

 the eyes are situated not on the sides but on the top of the head, and 

 the mouth is also directed upwards. Its instinct leads it to bury 

 itself in the sand so that only the eyes are uncovered. It lies in wait 

 in this way until a suitable victim comes within reach, and then snaps 

 at it with a sudden movement. But it also possesses a decoying organ, 

 a soft worm-shaped flap, which it protrudes from the mouth as soon 

 as little fishes draw near. They make for this bait, and are thus 

 caught. 



Such ingenious fishing, which is. quite suggestive of the human 

 method of catching trout with artificial bait, occurs in many predatory 

 fishes ; but in every case the fish acts instinctively, without refiection, 

 on becoming aware of approaching prey. The suitability of the 

 action to the end does not depend upon consciousness of the end, or 

 upon reflection, but is a purely mechanical action, performed in response 

 - to the stimulus of a sense-impression. 



This is best shown by the fact that the instincts may lead their 

 possessors astray^ which always happens when an animal is transferred 

 to an unnatural situation, to which its instincts are not adapted, so to 

 speak. The mole-cricket, which is in the habit of escaping pursuit by 

 burrowing in the earth, makes violent motions with the forelegs, even 

 if it be placed upon a plate of glass into which it could not possibly 

 burrow ; an ant-lion (Myrmeleo), whose instinct impels it to bore into 

 loose sand by pushing backwards with the abdomen, goes backwards 

 on a plate of glass as soon as danger threatens, and endeavours, with 

 the utmost exertions, to bore into it. It knows no other mode of 

 flight, and its intellect is much too weak to suggest any novel mode. 

 Even the mode of escape most universal among animals, that of 

 simply running away, does not occur to it; it acts as it must in 

 accordance with its inborn instinct ; it cannot do otherwise. 



The change of instincts in the different stages of development of 



