ARACHNIDA. 3 



tion, are wanting in the Insects; they occur ^principally in 

 animals with a cephalothorax, and are in three pairs. 



d. The true legs = feet (pedes) at least in three pairs, con- 

 sisting of a globular or cylindrical hip-joint (coxa}; the trochanter, 

 which is immoveably soldered to this; the thigh (femur], the 

 shank (tibia), and the multi-articulate /O0/ (tarsus). 



e. The false ventral or abdominal feet (pedes spurii, fausses- 

 pattes) on the segments of the abdomen, behind the true legs. 

 They are wanting in the Arachnida and Insects. 



/. In the higher species, the jointed appendages upon the 

 hack, the wings. Cilia are entirely deficient. 



6. A peculiar course of development. A clear distinction is 

 produced between the yelk and the germ-foundation from which 

 the embryo is formed, which is turned with its back towards the 

 yelk, and not with its ventral surface as in the Vertebrata, and 

 the organs of which are developed from the ventral side and 

 finally close towards the back. 



The Articulata are divided into four classes : I, Crustacea ; 

 II, Myriapoda ; III, Arachnida; and, IV, Insecta, of which we 

 are only interested in the last two. 



A. Class I. ARACHNIDA. 



Arachnida sunt Articulata inprimis cephalothoracica / in cepha- 

 lothorace, non in abdomine pedes, plerumque 8, gerentia et antennis 

 veris, quarum functiones per mandibulas aut forcipes venenatorias 

 exhibentur, carentia. 



We find only a cephalothorax with four, rarely with three 

 segments, or a single fused mass with oral organs ; with four 

 pairs of legs on the middle of the body; with the anus and 

 sexual orifice on the abdomen. 



In detail the Arachnida consist of the following parts : 



1. The skin consists of a soft, coriaceous, rarely brittle, exten- 

 sible, but not contractile, chitinous mass. It is rarely naked, 

 generally hairy, bristly, scaly, or furnished with jointed appen- 

 dages, and also with pigment-granules or vesicles. 



2. The legs consist of a roundish coxa with a short trochanter, 

 a powerful femur, a long tibia, and generally a two-jointed 

 tarsus, with or without claws. In the mites, the sections are 

 generally of equal size ; in the weaving spiders, the tarsal joints 



