BRITISH SPECIES OF PHALAXGlDEA OR HARVEST MEN. 165 



used in generation ; but this is never the case in the Harvest-Men, 

 whose palpi, though often varying much in form and development 

 in the two sexes, end similarly in both, with a simple claw ; their 

 method of generation is also totally and remarkably distinct. 

 Again, in spiders the basal joints of the legs are articulated to a 

 sternal plate of considerable size, while, though this is represented 

 in the Harvest-Men, it is of quite subsidiary importance and 

 generally difficult to observe ; the extremities of the legs are 

 also subdivided into many minute articulations. These external 

 differences are easily observed, and when we come to internal ones 

 it will be sufficient here to note one, that is that the respiratory 

 system is simply tracheal, and its external orifices quite differently 

 situated from those of the tracheae and Sac-trachese of spiders. 



Probably no one who attends fairly to the differences above 

 noted will mistake a Harvest-Man for a spider. Yet it might still 

 be difficult at first sight to distinguish some of them (the Trogulidcz 

 for instance) from some of the larger and longer legged Acarids, 

 especially some of the family Trombidiidce, but if it is remembered 

 that the latter never have the abdomen segmented, while that of the 

 Harvest-Man always is so, or at least shews its former separation 

 by transverse lines or grooves, there will be very little chance of 

 confusion. There are, of course, other striking differences between 

 the Order of Mites, or Acaridea, and the Harvest-Men, but the one 

 I have mentioned may suffice for our present purpose. 



In one of the most recent works upon this order, M. Simon divides 

 Harvest-Men Phalangidea (or according to his terminology, the 

 Opiliones} into three sub-orders, based on well marked structural 

 characters ; as, however, all our British species belong to one only, 

 the third Opiliones * " Plagiostetlii" there is no need, for our 

 purpose to go into this primary division. The whole group or 

 order Opiliones of Mons. Simon is co-extensive with my order 

 Phalangidea, which seems to me to be sufficiently sub-divided 

 directly into various families without the intervention of Sub-orders. 

 This is, however, a question of classification into which it is 

 * Plagiostethi fr. ir\dyios transverse arrjQos breast (sternum). 



