THE SENSES AND THEIR ORGANS. 319 



Another account of organs of stridulation in spiders is that observed 



by Mr. S. E. Peal in the great stridulating Mygale of Assam, and brought 



to notice by Prof. James Wood-Mason. 1 Mr. Peal's account is 



that the noise is made by the tarantula when in a state of great 



lans excitement, particularly at the presence of some enemy. When 



thus roused, the spider usually rested on the four posterior legs, 



raising the other four and shaking them in the air, with the thorax 



thrown up almost at right angles to the abdomen, and the palps in rapid 



motion. The noise made is both peculiar and loud. It resembles that 



made by pouring out small shot upon a plate from a height of a few 



inches, or perhaps by drawing the back of a knife along the edge of a 



strong comb. The stridulation was very distinct, and had a ring about 



it which the observer had never noticed in the stridulation of orthopterous 



insects, wherein it more closely resembles a whistling sound. 



Professor Wood-Mason, who reported Mr. Peal's statement to the London 

 Entomological Society, 2 remarks that the sound apparatus in Mygale stridu- 

 lans has been found to consist, first, of a comb composed of a number of 

 highly elastic and indurated, globe shaped, chitinous rods, arranged close 

 together on the inner face of the basal joint of the palp ; and, second, of 

 a scraper formed by an irregular row of sharp erect spines on the outer 

 surface of the penultimate joint of the palps. He further states that it 

 is equally developed in both sexes, the first specimen met with by Mr. 

 Peal having been a gigantic female. 



In the spiders alluded to by Westring, the . stridulating apparatus con- 

 sists, as we have seen, of a serrated ridge "at the base of the abdomen, 

 against which the hard hinder part of the thorax is rubbed, and of this 

 structure not a trace could be detected in the females. 



Professor Mason agrees with Mr. Darwin and Professor Westring in 

 feeling almost sure that the stridulation made by these spiders serves as 

 a call to the female. It is manifest, however, that if the sound serve this 

 purpose in the Mygale, it must serve as a mutual call, the apparatus being 

 present in both sexes. Professor Wood-Mason further ventures 

 ses o ^.j ie SU gg es ti on th a the sounds are emitted by the spider in self 

 lation defense ; that is, to render itself terrible in the eyes of its ene- 

 mies; or, it may be from fear. He thinks that they may also be 

 serviceable to the spider in terrifying its prey ; and, further, that during its 

 nocturnal rambles in quest of food, it may warn the creatures that it 

 preys upon of its dangerous and deadly nature, as, for example, is the 

 case with the rattles upon the tail of our American rattlesnake. 



Of course, the presence of stridulating organs, if they be regarded as 

 sound producing organs, naturally infers the presence of auditory organs. 



1 Proc. Asiatic Soc. Beng., 1876, and Ann. Mag. Nat. Hist., 1876. 



2 Transactions, 1877, page 282. 



