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Abstract

The structure o f the chelicerae was stuáied w ith seanning electron micros cope in th e tick Amblyomma cajennense (Fabricius, 1787). Lamellar organs were seen a t th e basis of the digits of th e chelicerae. Considerations on the palaeontologic origin of ticks anã Acari are made w ith reference to literature.The use of seanning electron microscope not only enables to complete th e description of well-known species and to define their spacial configuration more precisely, as was àone by ourselves anã o th e r s fo r the cephalic form ations of Nematodes (1,2,3), but also discloses ne-w form ations, as by Wooley (7> 8) for th e sense organs and respiratory ap p aratus of ticks. While trying to define more precisely th e chetotaxia of the palps and th e morphology of the chelicerae, we were led in exam ining various specimens of Am blyom m a cajennense. to discover th e existence of form ations undescribed h ith erto (4>. They seemed to bring argum ents on th e one han d for the conception of homology of th e chelicerae with th e m outh p arts of m andibulate or the other h an d for the possibility of considering Acari as th e m ost prim itive forms of Arachnids. MATERIALS AND METHODS Specimens of Amblyom ma cajennensewere fixed for 48 hours in the eth an o l/ chloroform /diethyl ether/acetic acid mixture. They were carried over to alum inium slide-cylinders and stuck on them with silver lacquer to secure the conductivity of th e é le c tr o n s . T h e s a m p le s w e re p J a c e d i n a vacuum evaporator w'here they were first coated ■mttv a t\\m oí tatboxv, IViexi •pYaX.eà w ith gold. Then they were examined with the Cameca MEB 07 seanning electron microscope. To m ake th e photographing of the m ediai aspect of the right chelicera easier, the digits of the left chelicera were rem oved. RESULTSInvestigations with the seanning elec tro n microscope enabled us to observe facts of several orders.The right pedipalp show long setae and the term inal cupule contains the 4th article with very short sensilla (Fig. 1) . The hypostome comprises two clearly visible parts ( Fig. 2 and 3) . The arrangem ent of the large denticles in three rows is quite clearly visible (Fig. 3) . The digits of the L a b o ra to ire d e P a ra sito lo g ie , U .E .R . C crdeliers 15, ru e de l'E cole de M édecine, 75, PA R IS VIe, FRANCE_ S u b m itte d f o r p u b lic a tio n o n 2.5.1975.