24 . NATURAL SCIENCE. July, 



eyes on the carapace. The cause of their migration from the middle 

 of this plate has never been explained, but it is possibly connected 

 with the peculiar habit of rubbing the mandibles backwards and 

 forwards to produce the stridulation, the end in view, if the expres- 

 sion may be pardoned, being the keeping of the ocular nerves clear 

 of the retractor muscles, which normally pass on each side of them 

 towards the hinder portion of the cephalothorax. 



Since the possible utility of the stridulating instruments in 

 spiders has been recently discussed in some detail in the pages of 

 Natural Science, it is unnecessary to do more than briefly touch 

 upon the same topic in connection with scorpions. Suffice it, then, 

 to say that since the organs that have been here described are 

 equally well developed in both males and females, and appear in the 

 young long before the attainment of maturity, there is no reason to 

 suppose that they are of a sexual nature, serving, like the chirrup of 

 the cricket or the call of the cuckoo, to inform the one sex of the 

 whereabouts of the other. If this were the case, we should expect to 

 find, firstly, that the organs were exclusively confined to one sex, or, 

 at all events, better developed in it than in the other ; and, secondly, 

 that they put in an appearance either just before or simultaneously 

 with the reaching of the adult stage. Again, in spite of the opinion 

 of many authorities, who maintain that the existence of a sound-pro- 

 ducing organ implies of necessity the existence of an auditory 

 apparatus in the same individual, we can only assert again that there 

 is not a particle of evidence that either the large spiders or the 

 scorpions can hear the sounds that their own stridulating organs 

 emit. All the available evidence goes to show that in these groups of 

 arachnids the organ is brought into use when its possessor is under 

 the influence of irritation or fright, exactly as in the case of the rattle- 

 snake's rattle. Like the snake, too, both the scorpions and the 

 spiders are furnished with highly-developed poison-glands, and it is a 

 well-known fact in natural history that animals so gifted are 

 frequently rendered conspicuous by bright and staring colours, so that 

 they may not be destroyed by carnivorous creatures in mistake for 

 other harmless and edible species. Nature, in fact, for purposes of 

 protection, has labelled them with her poison-badge ; and, apparently 

 with the same end in view, she has supplied the rattlesnake and the 

 large spiders and scorpions with a sound-producing apparatus, which, 

 when in action, serves as a danger signal to meddlesome intruders, 

 warning them to beware of hostile interference. But if, as has been 

 suggested, it is the function of these interesting organs to act in this 

 manner as an advertisement of the whereabouts and nature of the 

 species that possess them, it is surely clear that their existence 

 implies the existence of an auditory sense, not necessarily at all in 

 the performers themselves, but only in the enemies that might 

 otherwise destroy them. In exactly the same way it is absolutely 

 unnecessary, and indeed impossible, for the katipo {Lathrodectus scelio), 



