SPINNING-GLANDS IN PHETNUS. 277 



is no necessity to alter the classification in the way Laurie 

 proposes. 



The second point of interest with regard to this pair of appen- 

 dages on the first abdominal segment lies in the evidence they 

 yield us as to the original character of these limbs, which are 

 now, as a rule, throughout Arachnids reduced to mere scale-like 

 opercula, either fused in the middle line {Chernetidce) or free 

 {Scorpio and G-aleodes). We have here certain witness that these 

 limbs were once cylindrical appendages. The same conclusion 

 can also be arrived at for Thelyphonus, the genital operculum of 

 which is constructed on the same plan as that of Phrynus. In 

 addition to these facts, we have the filamentous genital organs of 

 the Phalangidse very probably also to be deduced from limbs. 

 When, further, on the second abdominal segment we have the 

 (? three-jointed) pectines of Scorpio, and, still further, ou the 

 fourth and fifth segments the four-jointed mamillse of certain 

 Aviculariidse, we have, it seems to me, fairly conclusive evidence 

 that the abdominal appendages of the Arachnida, which have 

 now so generally vanished, were jointed limbs like those of the 

 thorax. 



Whenever, therefore, among the vestiges of limbs on the 

 abdomen we get anything more than a flat scale-like structure, 

 it is not a leaf-like limb at all, but a typical filamentous and 

 sometimes jointed appendage. We conclude, therefore, that the 

 scale-like opercula (genital or stigmatic) of the Arachnida have 

 no connection whatever with the leaf-like limbs of Lhmdus. The 

 latter are most probably, it appears, persistent phylloj)odan 

 limbs*, while the former are the vanishing remains of jointed 

 filamentous limbs. 



Apart from all theories as to the origin of the Arachnida, the 

 evidence to hand tends to show that the primitive form possessed 

 a pair of jointed limbs with a pair of stigmata on every 

 segment, thoracic and abdominal ; and that, as above stated, there 

 was very little diff"erentiation among the segments. The speciali- 

 zation of the first six segments with their appendages for pre- 

 hension and locomotion, and of all or of some of the remaining 

 segments as a highly distensible vegetative sac, constricted ofl" by 



* Cf. Beecher, "Appendages of the Pygidium of Triarthms,'" Amev. Journ. 

 Sci. ser. 3, vol. xlvii. p. 298 (1894) ; and " The Systematic Position of the Tri- 

 lobites,'" Quart. Journ. Geol. Soc, Aug. 1894. 



