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ARTHROPODA 



Family Polydesmid;e — Juliformia with large free head and laterally ex- 

 tended dorsal plates. — Polydesmus complanatus has once been recorded as an 

 accidental parasite in the human ahmentary canal in Europe. 



Pathogenicity. — These parasites give rise to symptoms both direct and 

 reflex. 



CLASS III. ARACHNIDA Lamarck, 1815. 



Euarthropoda with two pre-oral segments, the first bearing 

 typical eyes, and the second antennae or chelicerae, and six post- 

 oral appendages, modified so as to function as jaws, but possessing 

 also a well-developed ramus, which may be a leg, palpus, or chela. 

 The primitive forms have branchial respiratory processes, and the 

 higher pulmonary organs. 



The Arachnid a are classified by Lankester into :■ — 



Grade A: Anomomeristica. 

 Grade B : Nomomeristica. 



Subclass L Pantapoda. 

 Subclass IL Euarachnida. 



Grade a: Hydropneusta. 

 Grade b: Aeropneusta. 



Section A: Pectinifera. 

 Order Scorpionidea. 



Section B : Epectinata. 

 Order L Pedipalpi. 

 Order IL Aranea. 

 Order III. Palpigrada. 

 Order IV. Solifuga. 

 Order V. Pseudoscorpions. 

 Order VI. Podogona. 

 Order VII. OpiUones. 

 Order VIII. Acarina. 

 Order IX. LinguatuHda (Incertae sedis). 



Details with regard to this classification may be obtained by 

 reference to Ray Lankester' s paper in the Quarterly Journal oj 

 Microscopical Science, 1904, vol. xlviii., p. 165. 



We have already considered the effects of the bites of the Scor- 

 pionidea, the Aranea, and some of the Acarina, and now it is neces- 

 sary to consider more particularly those which are parasitic, and 

 cause or spread disease. 



Two orders must be dealt with in some detail— viz., the Acarina 

 and the Linguatulida. 



ORDER ACARINA Nitzsch, 1818. 

 Synonym. — Rhynchostomi. 



Definition.— Degenerate Arachnida with the basal segments of the 

 second pair of appendages united in the middle line behind the 

 mouth, while those of the third, fourth, fifth, and sixth appendages 

 are widely separated, and take no part in mastication. The re- 



