92 ANNALS OF SCOTTISH NATURAL HISTORY 



margins form straight lines, the front margin of the carapace 

 is generally truncated. In other genera the side-margins 

 are more or less curved, and form a rounded or almost 

 pointed margin in front. Though always forming a single 

 piece, the carapace is in some genera transversely grooved 

 by one or two sinuous lines. Again, the carapace may be 

 beautifully smooth and polished, or it may be more or less 

 coarsely granulated or tubercled. The ej>es, when present, 

 are placed symmetrically on each side of the carapace near 

 the fore-margin, and their number — four, two, or none — has 

 been regarded as forming a useful aid for the purposes of 

 classification. But such classification is largely artificial, 

 for it has been found that allied forms have the eyes 

 present or absent, and when present they may be distinct 

 or indistinct, and either four or two in number. The 

 exceedingly minute mouthy adapted only for sucking, is 

 situated in front of the fore-body betv^een the chelicerce or 

 first pair of appendages. 



The hind-body is slightly elongated and rounded 

 posteriorly ; its anterior margin is united with the fore-body 

 along the entire terminal margin of the latter. There are 

 twelve segments, eleven of which are distinct and evident 

 from a dorsal aspect, the twelfth or hindmost segment being 

 evanescent. Both surfaces of the segments bear transverse 

 plates — those of the upper surface being termed tergites^ 

 and those of the under surface sternites — but the junctions 

 of the various segments and the sides of the hind-body are 

 free of any chitinous covering, and admit of the hind-body's 

 expanding and contracting considerably. In the case of 

 gravid females the plates of the segments are very distinctly 

 separated from one another. The genital opening is situated 

 behind the coxae of the fourth pair of legs, at the base or 

 anterior end of the hind-body, and the anus is placed in 

 the centre of the hindmost segment. 



The first pair of appendages, the chelicerce^ project 

 immediately forwards under the front margin of the cara- 

 pace. Each chelicera is of two pieces. The inne'r or basal 

 piece is the larger ; on this the smaller moves and forms 

 with it a pincer for grasping purposes. Under the micro- 

 scope the chelicerae are seen to be equipped with certain 



