626 AEACHNIDA. 



in its form approaches the spiders, as noticed by Latreille. 

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

 are eight simple e3'es on each side of the head. The sijecies 

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

 Lubbock, the antenna? are said to be "four-jointed, but with- 

 out a well marked 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 (cephalothorax) 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 sjyinnerets), 

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

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

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

 The head is without anteniiie, or compound eyes. The order 

 shows some analogy with certain Uipterous insects, especi- 

 ally when compared Avith the wingless Chionea and Nyctcribia, 

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

 to some of the lower Crustacea, as the 3'oung stages and em- 

 bryonic development are remarkably similar. The typical 

 forms of fhe 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, which 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 Crnstacea. 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 of Plate 10. — Fig. 1, Lepi^ma saccharina Linn?; Fig. 2, '.i 

 DeyeRria flavocincta Pack.; Fig. 4, 5, D. purjrurascens Pack.; Fig. G, 7, Isotortvi 

 plum'jca Pack.; Fig. 8, 9, Machilis variabilis Say. 



