230 MANUAL OF ZOOLOGY. 



are fertilised by the alternate introduction into the vulva of 

 the appendages of the two palpi of the male. Treviranus's 

 supposition that these acts are merely preliminary stimuli, has 

 received no confirmation, and is rejected by Duges, Westwood, 

 and Blackwall ; and with good reason, as the detection of the 

 spermatozoa in the palpal vesicles has shown. . . . Duges 

 offers the very probable suggestion that the male himself may 

 apply the dilated cavities of the palpi to the abdominal aper- 

 ture (of the testes), and receive from the vasa deferentia the 

 fertilising fluid, preparatory to the union. . . . Certain it is 

 that an explanation of this singular condition of the male ap- 

 paratus, in which the intromittent organ is transferred to the 

 remote and outstretched palp, is afforded by the insatiable 

 proneness to slay and devour in the females of these most 

 predaceous of articulated animals." (Owen.) 



The Spiders are oviparous, and the young pass through no 

 metamorphosis ; but they cast their skins, or moult, repeatedly, 

 before they attain the size of the adult. 



DISTRIBUTION OF ARACHNIDA IN TIME. The Arachnida 

 are only very rarely found in a fossil condition. As far as is 

 yet known, both the Scorpions and the true Spiders appear to 

 have their commencement in the Carboniferous epoch, the 

 former being represented by the celebrated Cyclophthalmus 

 senior from the Coal-measures of Bohemia. Spiders are also 

 known to occur in the Jurassic Rocks (Solenhofen Slates) 

 and in the Tertiary period. 



CHAPTER XXXVIII. 

 MYRIAPODA. 



CLASS III. MYRIAPODA. The Myriapoda are defined as articu- 

 late animals in which the head is distinct, and the remainder of 

 the body is divided into nearly similar segments, the thorax 

 exhibiting no clear line of demarcation from the abdomen. There 

 is one pair of antenna, and the number of the legs is indefinite. 

 Respiration is by trachea. 



In this class comprising the Centipedes (fig. 78) and the 

 Millipedes the integument is chitinous, the body is divided 

 into a number of somites provided with articulated appen- 

 dages, and the nervous and circulatory organs are con- 

 structed upon a plan similar to what we have seen in Crustacea 



