CHAPTER XXVIII 



ARTHROPODA 



Arthropoda — -Diplopoda — Acarina — -Gamasoidea — Ixodoidea — Trombidoidea 

 — Eupopoidea — -Sarcoptoidea — •Vermif ormia — Linguatulida — Crustacea 

 — Chilopoda — References . 



PHYLUM ARTHROPODA v. Siebold and Stannius, 1845. 



Bilaterally symmetrical metazoa, with well-developed body cavity 

 and heteronomously segmented body with hollow segmental appen- 

 dages, moved by intrinsic muscles and penetrated by blood spaces. 

 One or more pairs of appendages behind the mouth are densely 

 chitinized and turned inwards so as to act as jaws. 



The phylum Arthropoda is divided into the following grades and 

 classes by Ray Lankester : — • 



Grade A: Protarthropoda. 

 Class 1. Onchophora. 



Grade B: Euarthropoda Lankester. 



Class II. Diplopoda. 

 Class III. Arachnida. 

 Class IV. Crustacea. 

 Class V. Chilopoda. 

 Class VI. Hexapoda. 



The Onchophora, which includes the genus Peripatus, does not 

 concern us, but the other classes all contain species of importance in 

 medicine. 



CLASS n. DIPLOPODA Ray Lankester, 1904. 

 Synonym. — Chilognatha. 



Euarthropoda, in which the somites generally fuse after early development, 

 forming double somites, with two pairs of appendages, or present legless and 

 leg-bearing somites alternately. They are terrestrial, breathing by tracheae. 



The following orders are recognized: — (i) Juliformia; (2) Symphyla; and 

 {3) Pauropoda. We shall only consider the first. 



Order I. Juliformia — Diplopoda with two pairs of appendages on each 

 somite. — Two families of the Juliformia need be mentioned: — ■ 



Family Julid^e — Juliformia with large free head, without broad dorsal 

 plates. — Two species of Julus — -viz., /. terrestris L. and /. londinenensis Leach 

 — have been found as occasional parasites (accidental) in the human alimentary 

 canal in Europe. 



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