10 10 INSECTS AND ARACHNID A 



strongly developed in Hoplophora, which is a wood-boring creature. 

 In other families they are more commonly joined, forming a maxil- 

 lary lip with a flexible edge for sucking purposes. The maxillary 

 palpi vary greatly ; in the Sarcoptidce, Myobia, &c. they are anky- 

 losed to the lip ; in the Phytopti Nalepa is of opinion that they are 

 needle-like piercing organs, but these may well be the maxillae. In 

 some predatory forms, as Cheyletus, Trombidium, &c., they assume 

 great importance, being the raptorial organs ; in the first they 

 are extremely large and powerful and work horizontally ; they are 

 provided with a number of long chitinous spines and comb-like 

 appendages of a very singular character. In Trombidium the 

 ultimate joint is articulated at the base of, or part of the way down, 

 the penultimate, forming a species of chela. In Bdella the palpi 

 are long thin organs, carried upward and backward, and have the 

 appearance of antennae. The joints of the legs are from three 

 (Demodex) to seven (some Trombidiidce and Gamasidce) ; five is the 

 most usual number. They are terminated by a sucker as in the Sar- 

 coptidce, where it is often very large ; or by a claw or claws, or both 

 together. In some parasitic species the claws are developed in a 

 special manner for holding the hairs of the host ; thus Myobia has 

 the claw of the first leg flattened out so as to form a broad lamina, 

 which curls round the hair and presses it against a chitinous peg on 

 the tarsus ; Myocoptes has a similar arrangement on the third leg. 

 Both these genera contain species which are parasites of the mouse, 

 and easily obtained. In the Oribatidce, Tyroglyphi, &c. the legs 

 are all strictly walking organs ; but in Cheyletus, most Gamasidce, 

 &c. the firsfc pair are tactile, and not used in locomotion. The legs 

 generally correspond on the two sides of the body, but in Freyana 

 heteropus, an extraordinary parasite of the cormorant discovered by 

 Mr. Michael (Plate XXII, fig. 3), the second leg of the male is developed 

 to a much greater extent on one side than on the other, and is 

 supported by a different sternal skeleton on the two sides ; the 

 strangest fact is that it is not always the same side that is thus 

 developed ; it is usually the left, but occasionally the right. The 

 integument of the Acarina is almost always soft in the immature 

 forms ; in the adults it is hard and chitinised in the Oribatidce and 

 most Gamasidce ; partly so in the Ixodidce ; and usually soft in most 

 other families, and often minutely striated. The hairs and other 

 appendages of the integument of a similar nature are often very 

 characteristic and extraordinary. In the nymph of Leiosoma palma- 

 cinctum they are large scale-like processes of a Japanese-fan shape, 

 which entirely cover up and conceal the body of the creature ; a 

 leaf-like form is also common. In Glycijmagus plumiger they are 

 elegant plumes ; in some Sarcoptidce, e.g. Symbiotes tripilis, some of 

 the simple setiform hairs are three times the length of the body ; 

 in the Trombidiidce the body-hairs are often extremely fanciful. The 

 setiform hairs are the principal organs of touch, those on the front 

 legs being specially important. So sensitive are they that Cheyletus 

 and some Gamasids, which are predatory and capture such active 

 creatures as Thysanaridce, are entirely eyeless, and trust to the 

 tactile sense only. Haller was of opinion that certain specialised 



