56 BRAIN MECHANISMS AND LEARNING 



(i) Do any motor patterns and taxis components exist which are 

 developed in the individual independently of learning ? 



(2) Does the assumption made by ethologists hold true that motor 

 patterns which, by the comparison of species can be shown to be phylo- 

 genetically homologous, are independent of learning ? 



(3) What is the role of individual learning, (a) in changing or developing 

 the pattern itself and {b) in intcgratnig such innate elements, it any, into a 

 functional whole ? 



Albhio rats [Ratttis iion'c[^ictis Erxl.) were isolated from the age ot 11 to 

 21 days and raised in cages with a grill floor and given powdered iood. 

 Since, in the absence of nest material, rats often carry their own tails, 

 these were amputated in the experimental animals. In contrast to Riess, I 

 tested the rats in their living cages, snicc it has been shown that in rodents 

 placed in a new room, escape and exploratory behaviour predominate 

 over other activities. For the test, a rack holdnig 30 g. of crepe paper 

 strips was fastened on one wall of the cage. The room temperature varied 

 between 17' and 19 C. In this way, the ncst-building behaviour of ((7) 

 eighty-two virgin rats (2-3 months old), (/)) three pregnant rats and the 

 nest building and retrieving of {c) forty-two females, 4 months old, 

 immediately after parturition, were tested. 



Of group ((?) (subgroup i) thirty-seven animals had nothing else ni their 

 cage than the glass with powdered food, fastened on one wall, and the 

 phial with water hanging from the roof Eight of these animals started 

 nest building as soon as the paper was presented and four started within 

 an hour. Thirteen of the animals ran around with paper strips in their 

 mouths, and eventually let them fall, thus behaving as Riess described, 

 and six gnawed or played with the strips. They all built nests within 

 5 hours. The remaining six rats of group ((7) (subgroup i), however, did 

 not build a nest. Observations in the previous days had shown that 

 twelve of these rats had had definite sleeping places. All eight animals 

 that built immediately belonged to this group. I, therefore, conjectured 

 that the structural poverty of the experimental cage might have interfered 

 with the establishment of a definite nesting place. Indeed, this may have 

 hindered many experimental animals and made building in some cases 

 impossible. That some of the experimental animals built in two places 

 is evidence favouring this assumption. To facilitate the choice of a place, 

 I divided one corner of the cages of the other experimental animals 

 (subgroup 2) with a small vertical screen. Of forty-five virgin rats tested 

 in such a cage, thirty-three immediately started nest building behind the 



