COMPAEATIYE MOEPHOLOGY OF THE GALEODID.T:. 317 



The Spiders (fig. 8) show still further modifications : the labnim is round and fleshy and directed 

 downward ; it is opposed by a distinct labium also bent downward and formed by the anterior edge of 

 the sternal plate. The opposed inner oral surfaces are finely striated transversely, as in the Pseudo- 

 scorpions and Thclyphonidffi. The cosal joints of the pedipalps function as maxilhe on each side of 

 the mouth. We thus have, in the Arauese, the mouth placed more vcntrally than in any other Arachnid *. 

 Asa concomitant change, we have the chelicerae bent downwards from the almost directly forward position 

 which they occupy in most other Arachnids. The Aviculariidic, however, which have retained other 

 primitive features [cf. p. 311), still have the ehelieer<E pointing directly forward. 



The mouth-structures of the Arachnida seem to me, then, to be dedueible from a beak such as we 

 have in Ga/eodes, although there can be no doubt tiiat this particular beak is itself considerably 

 specialized. As we shall see in the section on alimentation, all these beaks and mouth-parts are 

 specialized for the straining of the juices crushed out of the prey by the chelicerie, and in some cases 

 by the pedipalps also. The basal joints of the pedipalps (in Scorpio those of the first and second limbs 

 as well) are as a rule specialized to prevent the escape of such juices and to conduct them towards the 

 mouth. The series of figures and diagrams illustrating the mouth-parts (PI. XXVIII. figs. 5, 7, 8) 

 also show the changing positions of the pumping-apparatus ; this will be discussed in detail in the 

 section on the alimentary canal. 



The Positions of the Eyes. — The varying jiositions of the ocular tubercle with the 

 median eyes are shown in PL XXVII. figs. 1, 3, 0. We gather, from the embryology 

 of Scorpio, that the eyes of Scorpio had originally the same anterior position, but that 

 they at a later stage travelled back along the suture, reaching their utmost limit of 

 backward movement in. a genus which takes its name from this fact {Opisthojjhthalmns). 



It is a curious fact that in most Scorpions and in some Galeodidge the line of the 

 suture runs over the tubercle. This can be explained only as a secondary acquirement. 



In addition to the median eyes, Galeodes lias one or two pairs of lateral eyes, which 

 appear, in many cases at least, to be rudimentary. Their position is shown in PL XXIX. 

 fig. 4, le (14). If the above account (p. 310) of the secondary origin of the anterior 

 dorsal surface of Arachnids is correct, the lateral eyes of the Arachnids are all either 

 secondary formations or else have wandered off from the ocular tubercle on to the 

 cephalic lobes {cf. section on the sensory organs, p. 318). 



Summary of the Modification of the First Segment. — We have, then, in the 1st segment 

 a pair of limbs (whicli will be described later), a pair of median and one or two pairs of 

 lateral eyes, a labrum and labium, together forming a beak with a mouth at its tip, the 

 labium being an anterior prolongation of the ventral surface. The present position of 

 these parts lias been brought about by the development of the first pair of limbs into 

 seizing-organs, which have travelled upward and forward from the sides of the mouth till 

 thev meet in the middle line above the labrum. The basal regions of these chelicerae 

 form the cephalic lobes, wliich cover the original dorsal surface of the segment and extend 

 backwards over the 2nd and part of the 3rd segments. The only part of the original 

 dorsal surface of the segment now visible is the ocular tubercle. The concomitant 

 travelling forward of the basal joints of the limbs of the 2nd segment to the sides of 

 the mouth has forced forward the ventral portion of the 1st segment till it has opposed 



* The position assigned by Steeker (67) to the mouth of Gibl/occUuni is clearly an oversight. 



