204 MANUAL OF ZOOLOGY. 



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

 is that an explanation of this singular condition of the male 

 apparatus, 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. The Mites, Harvest-spiders, and Book- 

 scorpions have been detected in amber. 



CHAPTER XXXVIII. 

 MYRIAPODA. 



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

 ticulate 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 antennce, and the number of the legs is always more 

 than eight pairs. Respiration is by trachece. 



In this class comprising the Centipedes (fig. 102) and the 

 Millipedes the integument is chitinous, the body is divided 

 into a number of somites provided with articulated appendages, 

 and the nervous and circulatory organs are constructed upon a 

 plan similar to what we have seen in Crustacea and Arachnida. 

 The head is invariably distinct, and there is no marked line of 

 demarcation between the segments of the thorax and those of 

 the abdomen. The body, except in Pauropus, always consists 

 of more than twenty somites, and those which correspond to 

 the abdomen in the Arachnida and Insecta are always provided 

 with locomotive limbs. " The head consists of at least five, 

 and probably of six, coalescent and modified somites ; and 

 some of the anterior segments of the body are, in many genera, 



