120 Ahdomen in Ricimdei 



the mechanism by wliich the abdomen and the cephalothorax are coupled together, that the 

 position of the former in this specimen was abnormal ; when these two principal divisions 

 of the body are coupled together, as they normally are, the first and second sternites are 

 completely hidden'. In the relatively large piece of soft skin, which exists between the first 

 and the second sternites the sexual orifice (PL VIII., fig. 2 g, o) is seen in the shape of a 

 broad transversal slit. 



Thus the sexual orifice is here situated between the first and the second sternites, but 

 in those orders to which Ricinulei are most nearly related, the sexual orifice is differently 

 placed, viz. either in the posterior portion of the second segment (Palpigradi) or at the 

 posterior margin of the second sternite (Pedipalpi, Ai-anese). The question might therefore 

 fairly be raised whether after all there may not also in Ricinulei exist one more segment 

 in the abdomen, in front of those we have seen, in which case the sexual orifice would be 

 placed behind the second sternite. ' We have had difficulty in examining this portion of the 

 abdomen in Gryptostemma, but we do not consider the existence of such a fiuther segment 

 probable, because, in that ca-se, the peduncle in Ricinulei would contain two entire segments, 

 but this would be without a parallel in Arachnida with pedunculated abdomen ; in some 

 Aranese a portion of the second segment enters into the peduncle ; but otherwise only one 

 entire segment is known to do so. 



The seventh, eighth and ninth segments (PL VII., fig. 1 q) are quite small and form a 

 small " tail." They are completely annular, not divided into tergites and sternites ; they 

 diminish gradually in diameter towards the posterior extremity, and can be drawn together 

 like a telescope. This is probablj' their normal condition, at least in the adults, in which 

 even the seventh segment is more or le.ss completely drawn back into the wide part of the 

 abdomen, so that the tail is visible only as a small protuberance, on which the posterior 

 margins of the eighth and ninth segments are discernible only by very close examination, 

 as two concentric circles. This is of course the reason wh}' these segments have been over- 

 looked by our predecessors except b}' Thorell, vvho, however, has interpreted them as 

 constituting a kind of anal segment. At the extremity of the ninth segment we find the 

 anus (PL VII., fig. 1 q, a) in the shape of a small transverse slit of which the upper border 

 is slightly emarginate ; but there are no other orifices in this segment, from which it is clear 

 that there are no such glands here as are found in Uropygi. 



Amongst the orders of Arachnida, four, viz. those of Pedipalpi, Palpigradi, Araneae and 

 Ricinulei, appear to be more closely related to each other than to the other six orders, viz. 

 Scorpiones, Chelonethi (Pseudoscorpiones), Solifugse, Opiliones, Acari, and Linguatulina, whose 

 relationships to one another, and to the four first-named orders, appear to us somewhat 

 obscure. One of the distinguishing characters which those four orders have in common is 

 the existence of a more or less developed, but always short " tail," consisting of three 

 segments, with reference to which we propose the general name of " Arachnida micrura " for 

 these orders. A few remarks on the structure of this tail in the other three orders may 

 therefore not be out of place. In none of these orders can the tail be telescoped as in 



' In that specimen of C. Karschii on which the cephalo- which we have dissected, they were not sufficiently strongly 

 thorax and the abdomen were separated, these two sternites chitinized to attract notice, 

 were lost, and in the young specimen of G. crassipalpe 



