10 Abdomen in Ci/jjhopJitlialmi 



Troguloidffi and Nemastomatoidse, more so in Ischyropsalidoidae, and still more reduced in Pha- 

 langioida?, especially in Phalangium and allied genera. In the two first-named families we are 

 able to point out nine tergites and nine sternites besides operculum anale, in the sub-family 

 Phalangiini {Phalangium and congeners) eight tergites and seven sternites, while in Ischyro- 

 psalidoidre and the sub-family Sclerosomatini we find the structure intermediate in various degree 

 between that met with in Nemastomatoidas and Phalangiini. We consider operculum anale 

 in all Opiliones as a terminal segment of which only the dorsal part is developed'. The result 

 is, that in Cyphophthalmi and in many Palpatores we count ten segments, all complete with 

 exception of the terminal one ; in many Palpatores the eighth, and especially the ninth segment, 

 is more or less reduced or has vanished ; in Laniatores we have found generally nine sternites, 

 and never more than eight tergites besides operculum anale ; but, nine sternites being present, we 

 think that abdomen in realit}' must be composed of ten segments. 



In all Cyphophthalmi cephalothorax and the tergites of the eight first abdominal segments 

 coalesce so as to form a dorsal shield, of which the posterior margin is turned a little downwards 

 to the under surface, in consequence of which the apparent posterior extremity of the body is 

 formed by the tergite of the eighth abdominal segment. The boundaries of these eight tergites 

 are marked by grooves which are all quite distinct, with the exception that the last of them is 

 somewhat indistinct in (the male of) Pettalus on account of the peculiar excavation near the 

 apparent posterior extremity of the body which distinguishes (the male of) this genus. The 

 tergite of the ninth segment and operculum anale are situated on the under surface of the 

 body ; the ninth tergite is, as a rule, quite short, of semilunar shape, and longer at the sides 

 than in the middle ; it is always movably connected with the dorsal shield (that is to say with 

 the eighth tergite) and with operculum anale, but it does not rarely — in Ogovia nobis (PI. III., 

 fig. 1 e), and Siro Latr. (PI. V., fig. 1 h and 1 i), but not in Parasiro nobis (PL V., fig. 2 g) — coalesce 

 with the two sternites, which apparently are the sixth and the seventh, but in reality are the 

 eighth and the ninth. With its posterior concave margin the ninth tergite embraces operculum 

 anale which is nearly circular. In front of the posterior margin of operculum, between it and the 

 so-called seventh, really ninth, sternite, anus is situated, marking the real, morphological, posterior 

 extremity of the animal. 



Apparently abdomen has only seven sternites, and to begin with we shall number them 

 accordingly. The " seventh " (really ninth) sternite is semilunar in shape and always very 

 small, in any case somewhat smaller than the ninth tergite, together with which it embraces 

 operculum anale. In Stylocellus (PI. I., figs. 1 b and 1 o) the " seventh " sternite is only slightly, 

 at the sides, encompassed by the ninth tergite, so that the latter only to a very small extent 

 touches the "sixth" sternite, but in Pettalus (PI. III., figs. 2 b and 2 g), Purcellia (PL IV., figs. 1 6, 

 1 i and 1 k), Siro (PL V., figs. 1 b and 1 i), and Parasiro (PI. V., fig. 2g), the ninth tergite reaches 

 fully round the sides of the " seventh " sternite, so that the lateral extremities of the former 



' Thorell was the first who, in 1876 (a, p. 458), was led by He was no doubt induced to do so by two causes, viz. that he 



•comparative studies to interpret operculum anale as the had not seen the position of anus in Stylocellus, and the 



tergite of the ninth segment in Op. Palpatores and Laniatores ; consideration that he then could count an equal numljer of 



but as regards Cyphophthalmi, he interpreted in 1882 (c, p. 23 tergites and sternites. Pocock, on the contrary (a, PL ii. fig. 



and 26, bis) operculum anale in Slijlocellus, as the last sternite, 12, and b, p. 289), pronounced that the operculum anale was 



although it much resembles operculum anale in Laniatores, an "anal sclerite." 

 and he counts consequently nine tergites and nine sternites. 



