Abdomen in Rlclnulel; its Conpli/i(/ with Cephalothorax 121 



Ricimilei. In PalpigracH the last segment is furnished with a long, thin, many-jointed 

 flagellum. The segments of the tail in the Palpigradi are not divided into tergites and 

 sternites, but this is not of any consequence, as equally no such division exists in any of the 

 other abdominal segments. Nor do the segments of the tail in Uropygi exhibit separate 

 tergites and sternites, and on the last segment are placed the orifices of two glandular bags, 

 which in Oxopoei are known to contain a liquid secretion smelling like acetic acid. It is 

 also on the last segment that we find a supra-anal appendage, which in Oxopoei has the form 

 of a long, raan^'-jointed flagellum, with a thick basal joint, whilst in Tartarides it forms a 

 short style, either undivided or exhibiting a few feebly-marked joints. In Amblypygi there 

 exists, as is equally well known, no supra-anal appendage on the last segment of the " tail," 

 which is comparatively short and broad, and of which the two iirst segments exhibit separate 

 tergites and sternites. The latter is not the case with the anal segment\ but on its dorsal 

 surface we find a large and broad, very movable free plate which covers the anus as a kind 

 of anal valve: the orifice in question is not seen till the valve is lifted up considerably. In 

 Araneai the "tail" is extremely small and placed as it were in a heap with the mamillae, for 

 which reason it is generally overlooked. For further details on this subject we refer to the 

 treatises by Simon (e, p. -t) and Sorensen (/), and shall only add in this place that it 

 is not always possible to point out all three segments of the " tail " in Aranese, which is 

 quite in keeping with the fact that in these animals the division of the abdomen into 

 segments has to a great extent disappeared. In some cases, however, they are all very 

 readily recognized, particularly in Orbitelari;e, for instance in a Nephila or a large Epeira. 



4. The Coupling of the Abdomen tvith the Cephalothorax. 



(PI. IX., figs. 1 /• and 1^.) 



The abdomen and the cephalothorax are coupled together by the following adaptation of 

 these two parts of the body and of the fourth pair of coxa^. 



The transversal ridge on the cephalothorax, which we mentioned above as forming 

 apparently the posterior margin of the cephalothorax, is a little concave on that side which 

 turns downwards (or forwards), and at the same time higher in the middle than laterally. 

 This side is altogether smooth, which is also the case with the surface of all those parts 

 of the abdomen and the coxse which play a part in the coupling. 



On tJie dorsal surface of the ahdomen (PI. IX., fig. 1/) we notice first of all a deep, 

 crescent-shaped groove on the confines of the second and the third tergites {d^ and d^), 

 which is deeper in the middle than towai'ds the sides. The posterior wall of this groove is 

 formed by the tergite of the third segment and almost perpendicular, whilst the anterior 

 wall, which is formed by the tergite of the second segment, slants upwards and forwards 

 almost in its whole length. The above-mentioned ridge, near the posterior margin of the cephalo- 

 thorax, fits into this groove. — On either side of the body the .sternite of the third segment 

 (PI. IX., fig. 1 (J I'') reaches a little further forward than the tergites of both the second and 



' This segment is not always easily observed. In Titano- Neophryims palmatus (Hbst.) Kraep. it is small (short) and 

 damon medius (Hbst.) Kraep. the dorsal portion of the anal easily overlooked, 

 segment (apart from the anal valve) is rather large, but in 



s. 16 



