SPIDEES AND MITES. 241 



tHs body and tlie side of the lens forms a ring-like 

 channel which is filled with an aqueous humour, and 

 into this projects a circular process of the thick pigment- 

 coat, which corresponds to the choroid, thus defining 

 the pupil of the eye, and at the same time confining 

 the lens to its proper situation. The margin of this 

 pigment-ring may be considered as an iris, and is of 

 various colours, as red, green, or brown in those species 

 which are active by daylight, while it is black at the 

 back of the eye. The nocturnal species have no dark 

 pigments, but are furnished with a curtain {tapetwm), 

 which reflects a brilliant metallic lustre, and makes the 

 eyes of these Spiders glare in the twUight, like those 

 of cats. 



It will be interesting to compare with this range of 

 eyes, the same organs in a kindred animal, the com- 

 mon Harvestman {Phalangium cornutum). Here in 

 the centre of the cephalo-thorax rises a short pillar, 

 which is crowned with two rows of conical points, with 

 polished black tips. On each side of the pillar is a 

 large black eye, hemispherical in form, and brilliantly 

 glossy, exactly resembling, indeed, those which we 

 have just examined. There are, however, only this 

 single pair which thus look out laterally, exactly like 

 the eyes of Birds. There is, indeed, a speck on each 

 side of the thorax, considerably removed from the eye- 

 pillar, just above the origin of the first pair of legs, 

 which has been mistaken for an eye ; but it is truly a 

 spiracle, or breathing hole. 



There are many other points of interest about this 

 Harvestman, such as the conical spines which stud the 

 head, body, and limbs ; the multitude of small bead- 

 like joints into which the foot {tarsus) is divided ; and 

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