8 Sternum 



Stermnn is rather long in Laniatores, as it always reaches as far behind as the anterior 

 margin of the fourth pair of coxae, and as the proximal extremities of the second and third 

 pairs of coxa3 are broader than in other Opiliones. Anteriorly sternum is continued into the 

 space between the lobi maxillares of the first pair of coxse, forming a labium stemale. The 

 distance between the genital orifice and the mouth is therefore greater in Laniatores than in 

 other Opiliones. Sternum is at the same time very narrow ; it is only in certain genera, of 

 Trisenonychoidae, that it expands at the posterior extremity as shown by Loman (/, pp. 525 

 ^528). In Palpatores, on the contrary, sternum is always short, but it shows a good deal 

 of variation in other respects. In Phalangioidw it is not separated from labium, but sternum 

 proper, that is, the portion which is situated behind lobi maxillares of the first pair of coxse, 

 forms a transverse approximately rectangular plate, which is almost entirely concealed by the 

 projecting plate of "arculi genitales " which we intend to describe more particularly in the 

 third chapter ; sternum is separated from this projecting part by a groove in which the skin 

 is soft. In Nemastomatoidae and Troguloidse (see woodcut fig. I) sternum is not separated 

 from the anterior transverse portion of "arculi genitales," but it is separated from labium^ 

 by a strip of soft skin. In Ischyropsalis sternum is separated from " arculi genitales " by 

 a groove with soft skin, but it is joined into one piece with labium ; the two together 

 form a plate of greater length than width, in shape resembling a trapezium rounded an- 

 teriorly, and firmly chitinized through the greater part of its extent. In Tm-acus E. S. sternum 

 is separated from " arculi genitales " by a curved transverse groove, and forms, together with 

 labium, a triangular anteriorly rounded piece ; sternum proper is soft, but the basal portion of 

 labium, which is not distinctly separated from sternum, is firmly chitinized. In Sabacon 

 E. S., Parasabacon nobis, and Tomicomerus Pav., sternum is separated from labium, but not from 

 " arculi genitales" ; it is proportionally large, broad, and almost soft. — As regards Cyphophthalmi 

 we may state at once that a labium sternale is absolutely wanting, and that hitherto nearly 

 all writers have generally ascribed to sternum a greater length than it possesses. Sternum 

 has mostly been described as reaching to the soft part of the mouth, whereas in reality it 

 never reaches so far forward as the middle of the proximal extremity of the second pair of 

 coxae^ In Stylocellus (PI. I., figs. 1 ^, 1 m, 2 c ; PI. II., fig.s. 1 c, 2 c, 2d) sternum is a very 

 small, but thick and firmly chitinized triangular piece, which posteriorly touches " arculi genitales " 

 (the frame which anteriorly and laterally encloses the genital orifice), whilst on either side it 

 reaches the proximal extremity of the third pair of coxse ; anteriorly sternum enters between 

 the proximal extremities of the second pair of coxifi. In Oc/ovia (PI. III., fig. 1 d) sternum is 

 quite as large as in Stylocellus ; although we have not had an opportunity of dissecting this 

 animal, we believe that it is thick and firmly chitinized as in Stylocellus, because the condition 

 of sternum seems to depend on whether the second pair of coxaj are movable or not ; and 

 they are immovable in Ogovia as well as in Stylocellus. In Purcellia (PI. IV., fig. 1 h and Ij) 



> In a preliminary paper published a long time after our mandibles. Finally he has overlooked labium sternale in 



text was written, C. Burner deals with many points in the Troiiulns, which was known many years ago, but he states 



morphology of Arachnida. We think that we are justified correctly that a labium does not exist in Stylocellus, a feature 



in confining ourselves to a few remarks. We are quite unable which, for the rest, had already been pointed out by TUorell 



to concur in his opinion on labium sternale : it is impossible {c, p. 22). 



with Borner (p. 441, figs. 6 and 7) to consider labium iu - It maj' be mentioned that Thorell writes in 1882 (c, p. 22) 



Araneae and labium in Amblypygi as not homologous with on Anepignathi: "Sternum nunc breve, nunc lougum; labium 



each other; furthermore it is impossible to follow him sternale nullum." According to this statement he says (p. 23), 



(figs. 5 and 7) iu considering a part situated in front of the on Stylocellus: "Sternum breve," while he (p. 24) desciibes 



mandibles in Uropygi as homologous with labium sternale and figures sternum in Siro corsicus as long, reaching from 



iu Aranese, as in the latter group it originates behind the arculi to the posterior margin of stomotheca. 



