The problem of memory and capability of abstraction and generalisation is discussed with special reference to investigations performed in the Zoologi- cal Institute of Munster during the last 15 years. The main statements are the following ones. When related species or races of the same species of different body size are compared the capacity 0/ learning and duration 0/ memory is positively correlated with absolute brain size. In some cases the absolute size of the brain seems to be more important than its special structure and the phylo- geneticallevel of the animals. The maximum of similar optical tasks mastered at the same time was: Octopus 3, trouts 6, Iguana 5, a giant race of domestic fowl 7, Indian elephant and horse 20. Normally, memory lasts a very long 1 time. A horse retained 19 of 20 optical tasks 1 /2 year, a carp one task more 1 than 20 /2 months. The capability of abstracting also depends upon the absolute brain size. Examples are given for the capability of abstracting with regard to sensa- tions of touch (experiments with a racoon) and to hearing (experiments with jackdaws and parakeets).