Abdomen 9 



sternum is of similar shape and position as in Stylocellus, but is relatively somewhat smaller ; 

 preparations treated with caustic potassium show that in this jrenus sternum is not firmly chitinized 

 but consists of thin pellucid skin. In Fettalus (PL III., figs. 2/ and 8 c) sternum is also of similar 

 shape and dimension as in Stylocellus ; we have not been able to ascertain by means of dissection, 

 whether it is firm or consists of soft skin ; but as the second pair of coxae are movable in 

 Purcellia and Fettalus, contrary to what is the case in Stylocellus, and as the lobi maxillares of 

 this second pair of coxae are very similarly developed in these two genera, we believe ourselves 

 justified in assuming that sternum in Fettalus is of a similar thin quality as in Purcellia. In 

 Siro (PI. Y., figs. If/ and \h) and Fanisiro (PI. V., figs. 2e and 2/) no real sternum exists; 

 none such is discoverable by external examination, and preparations of specimens of both genera 

 treated with caustic potassium show that the thin and extremely narrow sti'ip of skin, which 

 connects the coxa? of the second pair in the middle of the under surface of the body, is not 

 dilated posteriorly in any noticeable degree. In both genera the second pair of coxae are movable, 

 but the lobi maxillares of these limbs differ much ft-om those in Furcellia and Fettalus, in 

 size and still more in shape. 



3. Abdomen. 



The structure of abdomen in Opiliones is rather complicated and its morphology difficult 

 to elucidate, because several of the elements — tergites and sternites — composing it are either 

 so completely fused that they cannot be recognized without a comparative investigation of re- 

 presentatives of most families, or some of them have vanished completely in many forms. In 

 this long chapter we attempt to give a detailed description which leads to a new interpre- 

 tation of several of its parts. But in order to help the reader as much as possible, we thought 

 it advisable to begin with a summary of our main results ; then we proceed to the description, 

 numbering the sternites — and tergites — according to the earlier mode of counting ; we hope in 

 this way to lead the reader gradually to the moqjhological understanding of the facts we point 

 out. We begin with the Cyphophthalmi, because all the component elements of abdomen are 

 more easily observed in this than in any of the other sub-orders. 



The summary of our results may be as follows. The abdomen in C}']3hophthalmi consists 

 of nine complete segments besides operculum anale. The eight anterior tergites are fused with 

 each other, but, nevertheless, easy to count ; the ninth tergite is movably connected with the 

 eighth. The ventral side shows nine sternites ; the first sternite embraces, as " arculi genitales," 

 the genital opening on the .sides and in front; the second and third sternites constitute together 

 a large plate which is (le.scribed as the first sternite by earlier writers ; the spiracles are situated 

 in the second steniite, and the middle part of this sternite is produced forwards so as to form 

 operculum genitalo, which in this sub-order is immovable, redticed or sometimes quite rudimentary ; 

 the fourth to ninth sternites are generally all easily seen. In the two other sub-orders the anterior 

 ventral part of abdomen consists of the elements as in Cj7)hophthalmi : the large plate, generally 

 named the first sternite, consists of the second and third sternites, which often are marked off 

 fi-om each other by a transverse impression ; the first sternite is sometimes — in Laniatores — very 

 reduced, sometimes well developed as conspicuous " arculi genitales " ; in Phalangioidae these 

 arculi are composed of a large lateral portion marked off from the fourth pair of coxae by an 

 oblique furrow, and a middle portion in front of the genital aperture. In Palpatores abdomen 

 presents considerable differences in the four families, its posterior portion being less reduced in 



s. 2 



