96 ARACHNOIDEA. 



CASE The types of this group are the red spider of our hot-houses, 

 and the harvest mites of our fields. These form two distinct 

 sections ; the former consisting only of vegetable feeders, while 

 there is little doubt that the latter are predacious and carnivorous. 

 One would naturally expect from this that they should be easily 

 distinguished from each other, and so for the most part they are, so 

 far as general facies goes, the former being very minute semi- 

 transparent, and not what is called very loud in their colours : 

 white, pale yellow, pale orange, pale flesh colour, pale rust- 

 coloured, or pale red ; while the harvest mites are larger, velvety, 

 and opaque, rarely semi-transparent, and of the most brilliant and 

 decided colours, generally some shade of scarlet, vermilion, or 

 red lead, varied sometimes with black. 



Some species have seven joints in the leg, others only six; and 

 Koch has used that as a distinctive character for separating a 

 portion of the family from the rest. All have two claws to their 

 tarsi ; but the Tetranychi have them short, rigid, close together, 



Claw of Tetranyduis prunicolor. Copied from Du^es. Claw of Troiiibid.'um holosericeum. 



so as to look like a single claw, and much curved; the others 

 not so much so. The woodcuts show the forms of these claws. 

 The eyes have been used as a character, but they seem to have 

 no more than specific value. The comparative length of the palpi 

 and legs, as well as that of their different joints, has been more 

 reHed on, but this too fails to keep obviously allied species 

 together. 



