62G ARACIIM1>A. 



in its form approaches tlie spiders, as noticed by Latreille, 

 The four-jointed antennae are long and elbowed, while there 

 are eight simple eyes on each side of the head. The species 

 are found on the leaves of garden plants. In Papirias of 

 L'.ibbock, the antennae are said to be "four-jointed, but with- 

 out a well marlvcd elbow, and with a short terminal segment, 

 offering the appearance of being many-jointed. * 



SUB-CLASS II. ARACHNIDA. 



The typical forms of this order have the body divided into 

 two regions, the head-thorax (cephalolhorax) and abdomen. 

 The head is sometimes quite distinct, but is generally sunken 

 into the thorax, which bears four pairs of legs, while the abdo- 

 men has no organs of locomotion, though the abdomen is pro- 

 vided with three pairs of jointed appendages (the t^j^innerets) , 

 which are, however, homologous with the legs. The metamor- 

 phosis is very incomplete in the lower forms, while in the 

 spiders there is none at all after the animal leaves the egg. 

 The head is without antenna?, or compound eyes. The order 

 shows some analogy with certain Dipterous insects, especi- 

 ally wht'ii compared w^ith the wingless Chionea and Nycteribia, 

 and its lowest forms (certain mites) bear a close resemblance 

 to some of the lower Crustacea, as the young stages and em- 

 bryonic development are remarkably similar. The typical 

 forms of t*he order homologize too closely with the apterous 

 insects to allow them to be separated as a distinct class. "We 

 shall see below that the rank here assigned to the group ac- 

 cords well with their anatomical characters and habits. 



In some genera there is a decided line of demarcation 



between the head and the thorax, wliich is, however. Aery 



distinct during embryonic life, and we do not perceive that 



gradual transition from mouth-parts to swimming legs which 



obtains in the Crustacea. The order, however, has much 



lower, more degraded forms than the Myriopods even, as 



the genus Demodex testifies, which may recall readily certain 



intestinal worms. This we would consider as but an example 

 ♦Explanation op Plate 10. — Fig. 1, Lepisma saccharina Liun?; Fis- 2. 3 

 Degecria jlavocincta Pack.; Fig. 4, 5, D. jjurpurascens Pack.; Fig. (!, 7, Jsotom t 

 yyiw/rei/ca Pack.; Fig. 8, 9, Machilis vuriabilis Say. 



