Euarachnida — X ip ho sura. 
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Division B. — Embolobranchia. 
Order 1. — Scorpiones (Scorpions). 
,, 2. — Pedipalpi (Whip-scorpions and their allies). 
,, 3. — Palpigracli. 
,, 4. — Aranecce (Spiders). 
„ 5. — Solifugae (False Spiders). 
,, 6. — Pseudoscorpiones (False Scorpions). 
„ 7. — Podogonct. 
„ 8. — Opiliones (Harvest-men). 
,, 9. — Acari (Mites). 
Sub-class 2.— PYONOGONIDA. 
Sub-class i.— EUARACHNIDA. 
Both the prosoma (“ cephalothorax ”) and the opisthosoma 
(“ abdomen ”) are well developed in these Arachnida and are 
typically separated from one another by a praegenital segment, 
which generally disappears, however, in the adult. The prosoma 
is usually covered dorsally by an undivided carapace which 
is, however, sometimes segmented posteriorly. Its appendages 
number six pairs. The first pair (“ chelicerae ”) are often chelate 
or prehensile, whilst the second, third, and fourth pairs may also 
be chelate, but are usually feelers (palps) or walking legs. When 
fully developed, the mesosoma consists of six somites, which bear 
plate-like appendages in the aquatic species ; in the land forms 
these appendages are much reduced and modified or absent. 
The metasoma also typically consists of six somites, which are 
devoid of appendages. The mesosoma and metasoma are often 
fused to form an opisthosoma or “ abdomen,” and obliteration of 
segmentation often takes place. 
The Euarachnida are divided into two Grades : — 
Division A . — DEL OB BA NCHIA. 
The respiratory organs of the Delobranchia are of an aquatic 
type, all the large plate-like appendages of the middle region of 
the body (mesosoma), with the exception of the first, being 
furnished with branchial lamellae. There are two orders. 
Order 1. — Xiphosura (King-crabs). 
None of the appendages of the prosoma are paddle-like in 
form in the Xiphosura. The segments of the opisthosoma do not 
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