X Abstract 



single specimen, and no previous author had examined more than one specimen of any one 

 species, except in a single instance when two specimens were available. We have examined 

 externally all three species hitherto known, and also five new to science ; six of these 

 species are from trojjical West Africa, and two from tropical South America. We have seen 

 adult specimens of both sexes and young ones in various stages ; we have had also the 

 opportunity of dissecting an immature specimen ; thereby w^e have been able to point out 

 the characters of species and genera, and to elucidate the structure of the skeleton, the 

 mouth, the respiratory and sensory organs. Some of the more important points may be 

 mentioned. The structure of the mouth is rather similar to that in Thelyphonus; the mandibles 

 (" maxillaj " auctorum) are completely fused with each other and with the proximal part of the 

 labrum, but together with the labrum they can be moved a little. Of the labium sternale scarcely 

 more remains than a few very long setse ; in Tlielyphonus similar long setse are found inserted 

 in the middle line just behind the mandibles, but in both types they are difficult to find 

 without dissection. Earlier authors found only four or five segments in the abdomen, but 

 it consists in reality of nine complete segments, and the sexual opening is situated in front 

 of the second sternite ; the three posterior segments are small and generally completely 

 withdrawn into each other. The abdomen is stalked and can be coupled or hitched to the 

 cephalothorax ; both these parts of the body are generally coupled firmly together, but the 

 animal must be able to undo this coupling at pleasure, for instance when eggs are to be 

 deposited. The fastening is effected by a peculiar development of the second and third 

 abdominal tergites, the third sternite, the posterior margin of the cephalothorax and the 

 fourth pair of coxje, these parts forming together a rather complex mechanism well adapted 

 to the puqjose. Such hitching is unicjue among Arachnids (and, for that matter, among 

 Arthropoda) ; another unique feature is that the three antei'ior pairs of cox» are immovably 

 fused, while the fourth pair is movable. The animals have but one pair of spiracles, and 

 these are placed near the posterior extremity of the cephalothorax on a small piece of 

 chitine inside the lateral border of the dorsal shield and above the third pair of coxae. 

 From each spiracle a kind of sac takes its rise, and from the distal and the inner walls 

 of this sac a great number of thin tubes originate which do not ramify and are without 

 spiral thickenings ; these tubes proceed to all parts of the body and the appendages. We 

 point out that the oi-gans of respiration in Arachnids may be referred to two types : one 

 of these are tracheae, as those of the Insects, viz. richly and gradually ramified tubes with 

 spiral thickenings ; to the other type belong the so-called lungs together with trachea; of the 

 kind met with in Cryjjtostemma, or slightl}' ramified tracheae without spiral thickenings; the 

 different kinds of organs referred to the second type are found in nearly allied orders or within 

 the same order, often two of them in the same animal, and they are substituted one for 

 the other in various ways within the same order (Araneae), while respiratory organs of the 

 two main types are never found in nearly allied orders or within the same order (Acari 

 excepted). — Our investigation of the very complicated structure of metatarsus and tarsus of the 

 third pair of walking legs in the male renders it probable that the pairing is brought about 

 by spermatophores. — We prove that Ricinulei must be established as a separate order more 

 closely allied to the order Pedipaljii (especially ThelypJiomis) than to any other group ; finally 

 we arrange Pedijaalpi, Araneae, Ricinulei, and Palpigradi as a main division, Arachnida micrura 

 nobis, pointing out the essential characters of that division and of its four constituents. 



It is generally admitted that most Opiliones possess only one pair of eyes ; very few 

 cave-forms are known to be blind. Various authors have stated that in some forms more 



