CHAPTER XxX 
TRACHEATA 
ARACHNIDA 
BRANCHIATE 
Forms Trilobita—Olenus. 
Eurypterina—Lurypterus, Pterygotus. 
Niphosura—Limulus. 
( Scorpionida—Scorpio, Buthus. 
| Pseudoscorpionida—Chelifer, Obisiwi. 
Pedipalpi—Phrynus, Lhelyphonus. 
Solifuga—Galeodes. 
J Tetrapneumones— ygale, 
Forms * Atypus. 
Araneida fy ; . 
Dipneumones—Lpeira, 
Lycosa. 
| Phalangida—Phalangium, Gonyleptus. 
( Acarina—Jvodes, Sarcoptes. 
inguatulida. 
Ae A es atulida 
Forms Tardigrada. 
aan eo! | Pyenogonida. 
| 
| ate 
ARACHNIDA 4 TRACHEATE 
| 
| 
L 
CHARACTERISTICS.— Arthropoda with a cephalothorax (prosoma) 
marked off from the rest of the body by the presence of a carapace 
and bythe character of its limbs. The abdomen may be segnented 
or unseginented, and is sometimes divided into two regions, 
the mesosoma and the metasoma, the latter may bear a posterior 
spine. Four pairs of walking-legs are usually present. The 
breathing apparatus may take the form of branchiae adapted 
for aquatic respiration, or of lung-books, or tracheae for 
breathing air. An internal skeleton in the form of a plate, 
termed the endosternite, is present in many forms. The 
genital orifice is usually on one of the anterior segments of the 
abdomen. They are, with the exception of one order, bisexual. 
The Arachnida fall into three groups—those that breathe 
water, those that breathe air, and certain aberrant forms,— 
and the members of groups differ to a very considerable extent. 
