98 ON SOME COMMON SPECIES 



about, or I should say, " walks about " — for these beetles are very 

 deliberate in all their movements — with as much ease as if its 

 body was free ; and this, I think, tends to show that Megnin is 

 right in his belief that " the so-called parasites merely make use 

 of their host as a means of transport from one place to another.'' 

 If they really obtained their nourishment from the beetle, in the 

 case in point the creature ought to have been half dead. Besides 

 this, however, it is only through the membranous parts of the 

 beetle that they could do so, for their mouth-organs, though 

 powerful, could not pierce the hard, chitinous envelope, which in 

 Ulster will sometimes turn the point of a pin, and here they are 

 crowded on head, thorax, and elytra as well as on the under-side 

 of the body. Fig. i is a nymph of the old G. Coleoptratorum of 

 Latreille, one of a large number (between forty and fifty) that I 

 found on a Geotriipes stercorarius^ all of which had the division of 

 the dorsal plate, said by Megnin to be characteristic of the nymph. 



These mites are blind — or, at all events, have no eyes — 

 though it is quite possible they may be sensitive to light. They 

 have two maxillag, a pair of five-jointed maxillary palpi, and a pair 

 of mandibles armed at the end with pincers like a lobster's claw. 

 Fig. 2 is a sketch of the mandibles of a Gamasus. Those of 

 Uropoda are somew^hat similar, one difference, however, being that 

 the mandible of Uropoda ends in a point, the fixed part of the 

 claw extending far beyond the hinged joint ; while in Gamasus 

 they are nearly equal — a mentum, and a pair of seven-jointed 

 labial palpi. 



One interesting point about the members of this family is that 

 they appear to form a link between the eight legged Aracluiida 

 and the true insects, which have only six legs, for the details of 

 their anatomy belong to both these classes. 



In the true insects, the labial palpi are comparatively small, 

 generally much smaller than the maxillary palpi. In the spiders, 

 on the other hand, the labial palpi are very large ; in fact, have 

 developed into an extra pair of legs. But in the Ga7nasidce and 

 in the genus Uropoda this is shown very clearly ; the labial palpi 

 are midway between the two. They are greatly enlarged, many 

 times bigger than the maxillary palpi, and to a superficial observa- 

 tion look like legs ; but when carefully examined, are clearly seen 



