THESES, GASTON DE GAAL. 



33. Henceforward the systematical investigation of Bird-Migration 

 has to consider also the hibernating regions and their peculiarities,in order 

 to balance the knowledge in the breeding regions with those in the win- 

 tering regions: a condition necessary for understanding the whole 

 Phenomenon. 



34. A better knowledge of Bird-Migration depends in the first place 

 on a methodical working out of the whole chronicled material gathered 

 from all regions; further on the establishment of a uniformly working 

 system of observation, extending, for the present, all over Europe. 



35. Without interzonal observations there is no plausible answer to 

 the general progress of Migration. 



36. Only after having gained a sufficient knowledge of the whole 

 Phenomenon, with its constant deviations, according to species and 

 region, can we begin to give it a deeper biological foundation. 



37. All errors, contradictions and imperfections in the question 

 of the progress of Bird-Migration result from the following causes: 



a) That the matter has been treated speculatively, whereas it ought 

 to be treated by a merely inductive method. 



b) That from few data, which though inductive, are after all only 

 local, too general conclusions have been drawn. 



c) That too great importance has been assigned to only pretending 

 „Authority". 



d) That dilettantism played too great a part in the matter. 



e) That methodical work was avoided, instead of which uncri- 

 tical compilations were considered sufficient. 



GASTON GAAL de GYULA. 



„Among the factors to be taken into consideration in the observa- 

 tion of Bird-Migration, only operations based upon average figures pro- 

 mise positive results". („Aquila" VII. 1900. pp. 370 377.) 



02) 23 K9 



