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For in the first case the construction can be more simple than 

 in the second, where food has also to be chewed. In the latter case the 

 inner wall would have to be enabled to do so through the existence 

 of chitinous ridges, edges, knobby formations etc, and in order to 

 use these with good results, strong muscles are also required. 



We find sitnilar appliances in several groups of Arachnida, and 

 mention here as an example the »sucker" of mites, e. g. of 

 Pteroptus vespertilionis (fig. 2), and the more complicated one of 

 Argas reflexus (fig. 3). Though the construction is of the same 

 type, the organ of the former species consists of only three movable 

 chitine-walls, while in Argas these walls approach the sexangular 

 shape through bifurcation, and the dilatators are also doublé the 

 original number. Both animals have a thin layer of circular muscles. 



The transition to the pharynx of the Opiliones (fig. 4.) is now 

 easy enough. The six regular longitudinal ridges, which can be 

 moved by as many dilatators, and the thick layer of ring-muscles 

 will principally enable the apparatus to cause mastication, 

 although the power of suction is not excluded. 



Now let us return to the pharynx that is only fit for suction, 

 as in the Nematodes and Pycnogonida. 



In the former (fig. 5) we find only radial muscles, that are to be con- 

 sidered as dilatators. The elastic walls, three in number, are here anta- 

 gonistic, at least, circular muscles are not met with in these animals. 



And lastly we only find radial muscles in the proboscis of the 

 Pycnogonida (fig. 6), which, however, suffice for the expansion 

 and contraction of the lumen. The fibres attachecl to the centre 

 of the sides of the triangle, crook the walls, while those fixed 

 to the angles can straighten the sides and reduce the contents 

 of the triangle. The latter set of fibres do the same work as the 

 layer of circular muscles does in the preceding instances. 



Now, it seems to me very important that among this group 

 of animals one of the three antimeres of the proboscis, thè upper 

 one, is wanting, as in Rhynchothorax mediterraneus, discribed 

 by Don rn, which has only two lips, and is moreover distin- 

 guished by other peculiar deviations. We are therefore forced to 



