THE VALUE OF INSTINCT AS A TAXONOMIC 

 CHARACTER IN SPIDERS. 



ALEXANDER PETRUNKEVITCH, 

 PROFESSOR OF ZOOLOGY IN YALE UNIVERSITY. 



(Contribution from the University of Porto Rico.) 



The study of animal behavior under experimental conditions 

 has brought into sharp opposition the supporters of the idea of 

 the rigidity of instinct with the defenders of its plasticity. The 

 inability of the animal, especially of invertebrates to meet new 

 and unaccustomed conditions in human fashion has furnished the 

 chief argument in favor of the attitude of the modern school of 

 behaviorists. The interpretation of an animal as a machine acti- 

 vated by stimuli to reflexes with an outward appearance of intel- 

 ligence, yet without intelligent control of its actions has been and 

 still is sufficiently often discussed by both parties not to need 

 further discussion here. Some day I hope to put together for 

 print some observations on the plasticity of instinct in spiders, 

 which I have made gradually during the past years. For the 

 present I want to content myself with another aspect of the 

 problem. 



The discussion referred to above naturally centers round the 

 phenomena of individual behavior. Ascending from individual to 

 species and widening our observations to different geographical 

 regions and environmental conditions, influenced by our prefer- 

 ence for the one or the other school of behaviorism we lay stress 

 either on the individual modifications or the specific similitudes 

 of instinct. The same applies of course to generic and family 

 characteristics. The instincts of spiders are apparently par- 

 ticularly rigid in this respect and easily traceable to family 

 relationship in burrowing habits, snare construction, courtship, 

 mating and care of cocoon. Thus all representatives of the 

 family Argiopidae build orbwebs, all Lycosidae carry the cocoon 

 attached to their spinnerets, etc. In fact in the earlier days of 

 arachnology the habits were used for family or larger group dis- 



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