244 MANUAL OF ZOOLOGY. 



being passed through what are called the " spinnerets." Tliese 

 are little conical or cylindrical organs, four or six in number, 

 situated below the extremity of the abdomen. The excretory 

 ducts of the glands open into the spinnerets, each of which 

 has its apex perforated by a great number of minute tubes, 

 through which the secretion of theglands has to pass before 

 reaching the air. Many spiders, however, do not . construct 

 any web, unless it be for their own habitations, but hunt their 

 prey for themselves. 



As regards, the reproductive process in the Spiders, it appears 

 certain that the act of copulation, so to speak, is performed by 

 the males by means of the maxillary palpi, the extremities of 

 which are specially modified for this purpose. The testes are 

 abdominal, but the semen appears to be stored up in the 

 enlarged extremities of the- maxillary palps, which thus per- 

 form the part of the vesiculse seminales. " The most careful 

 observations, repeated by the most attentive and experienced 

 entomologists, have led to the conviction that the ova are 

 fertilised' by the alternate introduction into the vulva of the 

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

 position that these acts are merely preliminary stimuli^ has 

 received no confirmation, and is rejected by Dug^s, Westwpod, 

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

 spermatozoa .in the palpal vesicles has shown. . . . Dug^s 

 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 defejentia the 

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

 is that an explanation of this singular condition of the male 

 apparatus, in which the intrornittent 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 Cydophthalmus 

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

 known to occur in the Jurassic Rocks (Solenhofen Slates) and 

 in the Tertiary period. 



