NOTES ON MILLIPEDES. 27 



VII. Class Arachnida. 



In this class are included the Spiders, Scorpions, Mites, Ticks 

 and their relatives. 



These animals have no distinct head, the head and thorax 

 beings fused together, and the result of this union (called the 

 ,; cephalothorax ") and the abdomen may or may not be seg- 

 mented. 



Breathing is carried on by air-tubes, lung-books or both. 



The sexes are distinct individuals. 



There are no antenna?, such as exist in the insects, centi- 

 pedes and millipedes. 



The cephalothorax bears six pairs of limbs ; — 



1st pair (the mandibles) composed of 2 or 3 segments, acting 

 as seizing or biting organs. 



2nd pair (the chelce, or palpi) composed of 5 or G segments ; 

 of which the basal segments (the maxilloe) are used for crushing 

 food, and the remainder variously modified as seizing, feeling or 

 sexual organs. 



3rd pair, composed of 6 or more segments, used for feeling 

 (as in the Pedipalpi), or for walking'. 



•4th, 5th. and 6th, composed of 6 to 9 segments, used for 

 walking. 



The abdomen bears no true limbs. 



The class may be divided into 8 orders, one of these con- 

 tains the Mites. Ticks and a varied host of small forms, some 

 Aery degenerate, in some various limbs are lost, in some there 

 are apparently no organs of respiration, and in the " Water 

 Bears." or Tardigrade the sexes are not distinct but are united 

 in each individual. 



The following table may be of use 'to the collector in 

 determining to which Order an Arachnoid beast, he may hap- 

 pen to have caught, belongs. 

 A. 2nd pair of limbs modified into great seizing organs (chelce). 



A. no " waist " between caphalothorax and abdomen. 



3rd, 4th, 5th and Gth pairs of limbs of similar con- 

 struction and used for walking. 

 (/. posterior segments of abdomen narrowed, forming a 

 distinct jointed tail, ending in a poison- sting. 



