128 Comparison hetween the Moutli in Ricinulei and Oxopoei 



by their integuments, a covering of long hairs, and the absence of muscles, whilst a 'pars basalts, 

 which contains a complicated set of muscles, is firmly united to the mandibles, and together 

 with the latter apparently is continued backwards into the head of the animal behind the 

 thin membranous skin which extends upwards and encloses the antennae. Although the 

 mandibles and the pars basalis of the labrum are firmly united together, there is no difficulty 

 m distinguishing them as sejjarate pieces. The principal differences between the structure 

 of the mouth in Cryptostemma and that in Uropygi appear to be that, in the latter, only 

 about one half of the pars basalis labri is as it were " inside," and that a triangular process, 

 in which the mandibles terminate, reaches laterally much further back than the pars basalis 

 labri. Thanks to the larger size of Thelyphonus we have been able to ascertain how this 

 appearance of the basal portions of the labrum and the mandibles being located inside 

 the head comes about. As in the case of the antennae we were able to show that it originates 

 from a folding of the skin. This skin is membranous above the posterior end of the labrum 

 and the mandibles ; it turns forward, lying very close to the dorsal surface of the " inner " 

 part of the labrum and mandibles, and reaching in front to that place — the transverse line (I) — 

 where it suddenly turns upwards to the antennte. We were able to introduce a fine scalpel — 

 with the end rather blunt — between the hard upper surface of the labrum and mandibles 

 and this membranaceous skin without injuring the latter. We have already mentioned that 

 as regards Gryptostemma we have had opportunity of dissecting only one, and that a rather 

 small .specimen, and on it we have not been able to manage the same operation ; but we 

 have not the smallest doubt of the structure being the same, in that genus, as in Thelyphonus. 

 The chitinous crest which extends downwards from the inside of the dorsal integument of 

 the labrum in Gryptostemma does not exist in Uropygi. 



Whilst the dorsal surfece of the parts of the mouth is essentially alike in Cryptostemma 

 and in Uropygi, their ventral surface exhibits greater differences. In the first place the 

 mandibles in Thelyphonus reach somewhat further back on the ventral than on the dorsal 

 side, whilst in Gryptostemma (PI. VII., figs. 1 k and 1 I) they reach much further back on 

 the dorsal side than on the ventral ; in the next place the mandibles in Uropygi are without 

 the posterior prolongation which in Cryptostemma (PI. VIII. , fig. 4 b) extends above the second 

 pair of coxEe ; the consequence of the last-mentioned fact is that the piece formed by the 

 coalescence of the mandibles and the labrum is capable of much more extensive and freer 

 movement in Uropj'gi than in Cryptostemma. 



It has indeed been stated by previous writers that the mandibles in Cryptostemma coalesce 

 with the coxa; of the legs. But it is quite certain both that this is not the case and that 

 the mandibles together with the labrum collectively are capable of some movement, viz. a kind 

 of swing by which the anterior extremity of the mandibles is moved a little up and down. 

 The axis on which the parts turn is a horizontal line drawn across the broadest part of the 

 mandibles, that is, on the upper side just in front of the place of insertion of the pair of 

 long tendons of m" (Pi. VII., fig. 1 Jc) which terminate the upper pair of muscles. Contraction 

 of these muscles must raise the anterior end of the mandibles towards the antennae, whilst 

 the opposite movement is effected by that pair of muscles (fig. 1 k, m7) of which the long 

 tendons are attached to the posterior extremity of the ventral surface of the mandibles. 



One more fact must be mentioned which clearly points to a close relationship between 

 Ricinulei and Pedipalpi, especially Uropygi. In Amblypygi the mandibles are, as is well 

 known, unconnected with each other, and movable independently of each other. It is 



