528 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



avoidance of danger, fighting, and reproduction. Activities of this 

 nature are mostly direct reflexes to stimuli and might be termed 

 instincts of intrinsic hehavior because they have to do with the welfare 

 and life of the individual. On the other hand, many animals have 

 constructive instincts for nest-building, cocoon-spinning, web-making, 

 etc. Such instincts may be distinguished as instincts of extrinsic 

 'behavior. They are comparable to tool-making, house-building, and 

 the manufacture of mechanical appliances by the human species. As 

 a third class of instincts we might include the migratory drive of some 

 animals, such as that of the eels, the salmon, many birds, and some 

 insects. 



Intrinsic behavior is common to all animals, varying according to 

 the habits, structure, and sensory equipment of each species. Ex- 

 trinsic instincts are most highly developed in the insects, spiders, 

 birds, and some mammals. It is of particular interest because the 

 constructural procedure of the animal often closely resembles human 

 workmanship, and yet is unlearned and acquired by heredity. 



Examples of extrinsic instinct among the insects are so well known 

 they scarcely need to be cited. They include the familiar cocoon- 

 spimiing of the caterpillars, nest-building by the wasps, comb-making 

 by the honey bees, and the construction of above-ground nests by some 

 termites. 



The spiders have long been famous for their spuming of silken 

 webs. The types of webs vary from the too familiar formless mass of 

 threads spun by the house spider to the flat orbs of the outdoor garden 

 spiders. Each species of the latter, as noted by Crompton (1950), 

 builds one fixed pattern of web, but the talents of the different species 

 vary. A relatively simple example of a flat web is that of Hyptiotes 

 paradoxus^ which is a triangle with two inner radii diverging from 

 the apex, and the interradial spaces filled with cross-threads. The 

 spider's method of making this web is described in detail by Peters 

 (1938), who shows that the spider follows a complex but entirely 

 orderly plan of construction. Clearly she "knows" in advance what 

 the completed web must be like and exactly how to make it. As many 

 separate acts are involved as there are threads in the web, and yet the 

 spider goes from one to the next as if she carries the whole plan in her 

 mind. Still more elaborate and complex are the orb webs of Araiiea, 

 but even in the spinning of these webs the spider is just as competent 

 and methodical as Hyptiotes. 



A human workman making a fabric as intricate as a spider's web 

 would have to learn in advance how to do the job, or he first would 

 work out a plan in his mind or on paper. Then he would consciously 

 direct the action of his arms and fingers for each phase of the work. 

 The spider, on the other hand, never learned how to spin a web, or 

 how to make one of the particular pattern characteristics of her 



