2'jS Alexander Petrunkevitch 



the organs of copulation in the male, are entirely separate from 

 the internal sexual organs. If we may judge of the amount of 

 food required by the quantity of insects captured in the orb-net 

 of a single spider, a quantity that is sometimes appalling, it was 

 necessary for the spiders, in order to satisfy this want, to develop 

 as they indeed have done, either the instinct and the engineering 

 capacity for constructing nets or else the instinct for hunting their 

 prey freely on the ground or on plants. Two different directions 

 are thus given to the development of the whole spider group and 

 we should naturally expect to find differences in the structure of 

 the corresponding organs of sense and of the spinning apparatus. 

 But while in higher animals, as for example, birds of prey, all 

 organs of sense are developed to a remarkable degree of perfection, 

 we cannot say the same for the hunting spiders. It is a matter 

 of common observation that vultures discern their prey from a 

 distance amounting at times to several thousand feet and they 

 are undoubtedly able to scent a carcass hidden among bushes 

 at a considerable if not so great a distance as this. Their ears 

 are sensitive to high and low sounds of a very small amplitude 

 and only the sense of touch which could scarcely be of use to them, 

 is little developed. It is otherwise with the hunting spiders. 

 They possess doubtless, a very fine sense of touch, the whole body 

 being covered with hairs and bristles sensitive to the slightest 

 stimulus. In regard, however, to the organs of hearing and 

 smell we are as yet without definite results of any kind. At any 

 rate these two senses are very little developed. Even the ques- 

 tion as to the existence of such organs is to my mind far from 

 being settled. Whether the organs discovered by Dahl and the 

 lyriform organs have anything to do with these senses must be 

 determined by new investigation. I myself have made some 

 experiments on the sense of hearing, thus far without any definite 

 results. I also repeated the experiments of Pritchett on the sense 

 of smell in large lycosids but even to such irritants as formalde- 

 hyde, osmic acid and acetic acid, they did notrespond soreadilyor 

 so quickly as to the slightest touch with the end of a silk thread. 

 As the sense of touch is solely protective, there remains only the 

 sense of sight to guide the spiders on their hunting trips. The 



