32 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



consisting of six (rarely eight) 

 somites. Mandibles chelate. Legs 

 veiy long and attenuated. Tra- 

 cheal tubes with one pair of spira- 

 cles between thorax and abdomen. 

 X Leiobunum, Phalangium. 



Order 4, Arachnida Abdomen unsegmented, swollen, 



and attached to cephalo-thorax by 

 a stalk. Mandibles end in a 

 simple claw with poison gland. 

 Second pair of appendages leg-like, 

 modified in male. Two to three 

 pairs of spinnerets at end of abdo- 

 men. One to two pairs of ' ' lungs ' ' 

 situated on abdomen. These may 

 be also connected with a system 

 of tracheal tubes. 



X Epeira, Agalena. 



Orders. Acarina Abdomen fused with cephalo- 

 thorax; body unsegmented; ap- 

 pendages about mouth often 

 modified to form a sucking tube ; 

 respiration by tracheal tubes or 

 merely through integument ; many 

 parasitic forms. 



X Ixodes, Tyroglyphus. 



There are several other Orders of Arachnoidea, but they are confined 

 to the Tropics and of interest mainly to specialists. 



Supplementary arthropod groups (doubtfully referred to the 



Arachnoidea). 



Pantapoda (Pycnogonida) Extremely attenuated marine forms 



with long slender legs and body 

 of about the same diameter. 

 Cephalo-thorax of six segments, of 

 which the first are fused and possess 



