18 ARKIV FÖR ZOOLOGI. BAND 2. N:0 8. 



or by dissection, another but very low, rounded ridge is ob- 

 served produced by a träns verse folding of the thin skin 

 about at the middle between the hind margin of the sternite 

 and the front end of the lower wall of the trunk. The in- 

 vestigation shows that the last-named ridge is (about as 

 in Oxopoei) the real front boundary of the spirade. Posteri- 

 orly (above) the spirade is Hmited by a träns verse rather 

 thick ridge formed by a folding of the skin in front of the 

 following sternite; this ridge is overlapped below by the po- 

 sterior part of the preceding sternite. A longitudinal yertical 

 section shows that the shape of the trunk is intermediate 

 between those in Scorpiones and Aranese: the posterior side 

 of the triangle is directed more backwards t han in Araneae 

 but less so than in Scorpiones; the lower side is very short. 

 The margins of the »pouches» at their origin are scarcely 

 more chitinized than their walls. 



In Oxopoei — among which Thelyphonas caudatus (L.) 

 Thor. has been studied — the spirades are, as is known, 

 placed between second and third, and between third and 

 fourth sternite. The places of the »lungs» and the spirades 

 can not be discerned from the outside without rather vigorous 

 manipulation. As some slight difference in the two pairs of 

 organs is observed, each pair is to be mentioned separately. 



The second pair of spirades are seen when the sternites 

 of third and fourth segments are removed by dissection and 

 bent from each other. It is bounded in front (below) by a 

 low but yet distinctly raised ridge placed a littie in front of 

 the posterior margin of the sternite; this ridge is a duplica- 

 ture of the rather thin skin originating from the hind margin 

 of the sternite and folded forwards above its posterior part; 

 the ridge is scarcely more firmly chitinized than the surround- 

 ing skin. On a longitudinal vertical section the ridge shows 

 a nearly regularly triangulär shape; it is of the same height 

 in nearly its who]e length, while its free margin is a littie 

 concave. Above (posteriorly) the spirade is bounded by a 

 sharp ridge, formed by a duplicature, the posterior side of 

 which is the front part of fourth sternite curved downwards 

 and strongly chitinized, while the anterior, front, side is rather 

 thin-skinned ; the free margin of this low ridge is feebly 

 convex. It can not be doubted that the animal is able to 

 open or shut the spirade by a small movement of the ster- 



