IRENAUS EIBL-EIBESFELDT 63 



behaviour of the animal in the test situation. It the author had followed the 

 same line when studying the prey-killing behaviour of the polecat, he, too, 

 would have come to the conclusion that this specific technique is learned, 

 since the animals need several trials before killing efficiently. But the 

 crucial point is that it does not need to learn the shaking movements and 

 it does not need to learn to attack and grasp a fleeing object. If one observes 

 the behaviour one finds that a number of movements are there from the 

 moment the first reaction towards prey is released. Kuo's (1930) experi- 

 ments on cats do not contradict our experiments, but simply fail to give 

 information on certain important questions. The results of Riess, on the 

 other hand, clearly contradict our observations, due to the fact that Riess 

 made the methodological mistake of testing his animals in a surrounding 

 strange to them. The immediate nest building of our inexperienced animals 

 can hardly be explained by the learning hypothesis. How should our rats 

 have learned that nesting material keeps the animal warm if collected 

 and formed into a nest? And what taught the mother that newborn nest- 

 lings need to be covered with nesting material, and that straw has to be 

 split? 



3. DISCUSSION OF THE CONCEPTIONS 



According to Lorenz (1952) fixed motor patterns are sequences of 

 movements which can appear in an animal without previous exercise and 

 experience. Presumably they are based on specific central nervous 

 mechanisms, which are inherited in the same way as other morphological 

 structures. The characteristics of fixed patterns are: 



(i) They are constant in form. 



(2) They are characteristic for the species. 



(3) They appear in an animal reared in isolation from members of its 

 own species. 



(4) They develop even if the animal is prevented from exercising the 

 behaviour pattern in question. 



(5) They are hardly ever found in one species alone at least if closely 

 related species are in existence, but are characteristic of taxonomic groups 

 just as morphological characters are. Thus can they be used for taxonomic 

 purposes, as has been shown by Heinroth (191 1), Whitman (1919), 

 Lorenz (1941) and others. 



Our experiments have shown that in every case in which, on the basis 

 of criteria gained by comparative observation alone, a sequence of move- 

 ments was suspected of being a fixed pattern, the co-ordination in question 



