ENGINEERING SKILL OF SPIDERS. 215 



taut to capture prey, as indicated by the number of victims entangled in 

 its meshes. It was so firmly implanted, and so opportunely repaired, that 

 Prof. Parona was able to observe it continuously for eight days. The in- 

 terest of the observer was so much enlisted in what seemed to be an inter- 

 esting and novel fact, that he made various inquiries and researches as to 

 previous records. 



Among others, he communicated his observation to the veteran arach- 

 nologist. Professor Thorell, requesting his opinion thereupon. The ques- 

 tion was submitted by Professor Thorell to myself, as lying 



"Pt* O I f-* ^ ^ O T* 



_^ within the line of my special studies of life habits, and I re- 



Parona. . 



turned for answer substantially some of the facts which have 

 been recorded in this chapter. Nevertheless, Professor Parona has done 

 well to place his observation upon record, and he has fortified it by like 

 observations from other authors. Among these is the experience of Pro- 

 fessor Pavesi, in part as above. He quotes a second observation in the 

 same line made by Ninni, on the web of Epeira umbratica, as recorded in 

 the Acts of the Society of Natural History of Veneto-Trentina. ^ This 



spider wove her snare under the roof of a beehive, and gave it 

 Bpeu'a stability by carrying down a thread to the soil and wrapping 



it around a pebble which was raised to the height of about 



seven inches (about eighteen centimetres) from the ground. De- 

 siring to know if such ingenious work were confined to that case, the 

 author destroyed the web and waited to see how the spider would behave 

 in the face of the difficulty that it had previously overcome. Three days 

 afterward he saw the web built in the same manner as before, but more 

 perfectly finished. As though conscious that without another point of at- 

 tachment the construction of her snare would be im})ossible, the spider 

 carried down a thread which was maintained in a taut condition, not with 

 one pebble as before, but with two })ebbles and a straw. From this line, 

 as an initial foundation line, she constructed the framework of her orb in 

 the shape of an isosceles triangle, within which the orb was spun, in a 

 position well sheltered from wind and rain. In order further to test the 

 matter, the author destroyed this second web, but awaited the spinning of 

 a third one in vain, as Umbratica abandoned the site. 



It is to be observed that in tliis case also the testimony is defective, 



in that the observer did not see the spider actually using the pebble as 



. a counterpoise; that is to say, in the act of suspending it upon 



" the line. In ])oint of fact, what possible benefit could liave 



been obtained from staying the orb by a pebble hanging above the ground, 



when an attachment to the solid earth below in the usual manner, or to 



^ Sopra la tx»la (k'H' Epeira iimbratira: Atti Soc. Veneto-Trcntina di 8c. Nat. Padova ; 

 1876; Vol. 3, pages 204-5; Tav. YI. e \II. T regret that the particular number of this jour- 

 nal in Avhich the reference is made doi's not liai>i)en to be in the library of our Academy 

 of Natural .Sciences, and I have not, therefore, been able to consult the original. 



