632 AKACIIXIDA. 



The testes of Ixodes consist of four or five pairs of unequal 

 follicles, opening out near the base of the abdomen." The 

 males are distinguished from the females by their larger "cheli- 

 ceres" (maxillary palpi) and larger pair of clasping legs. In 

 the spiders the testes are "two long, simple, interlaced caeca, 

 concealed beneath the hepatic lobes," which lead by two def- 

 erent canals to the base of the abdomen, through a simple 

 fissure, which, however, is not applied to the vulva. The com- 

 plicated hollow spoon-shaped palpi are supposed to be the in- 

 tromittent organs. " They are filled with sperm and applied to 

 the entrance of the vulva. For this purpose the last joint of 

 the palpi, which is always hollow and much enlarged, contains 

 a soft spiral body, terminated by a curved, gutter-like, horny 

 process. Beside this there is an arched, horny filament, and 

 several hooks and other appendages of the most varied forms. 

 These appendages are protractile and serve, some to seize the 

 female, and others as conductors of the sperm." (Siebold.) 

 While the majority of the Arachnida are developed as usual 

 after the laying of the eggs, a few, such as the scorpions and 

 Oribatidce and other mites, are known to be viviparous, 

 and it is probable that an alternation of generations occurs in 

 some of the lower mites. The Tardigrades are hermaphro- 

 dites. 



The Arachnida breathe both by tracheae and lung-like organs. 

 The mites, the false scorpions, the harvest-men and Solpu- 

 gidce are provided with tracheae, communicating externally 

 by means of spiracles, generally two in number, and concealed 

 between the anterior feet. In Hydrachna, which lives con- 

 stantly beneath the water, the trachea "possess probably, the 

 power to extract from the water, the air necessary for respira- 

 tion." (Siebold.) In the false scorpions a pair of lateral stig- 

 mata are situated on each of the two basal rings of the 

 abdomen. From these spring "four short, but hir^v tnu-hean 

 trunks from which arise numerous unbram-hrd trat'luw spread- 

 ing through the entire body." In the SolpvgfdcK there aiv 

 three pairs of stigmata and the tracheae ramify and are distrib- 

 buted much as in insects, and in the Phalangidce the tra- 

 cheary s} r stem is well developed, arising from two stigmata 

 opening between the insertion of the posterior legs. 



