ARTHROPODA 



225 



prominent and vary in complexity from the small organ of the worker 

 of the ant, Solenopsis. which lives underground and is provided with 

 6 or 8 facets, to the elaborate organ of dragon-flies (Odonata) with up 

 to 28,000 1 ommatidia (Imms, 1935) (Figs 225 to 227). Occasionally 

 the compound eyes are enormous, literally occupying the whole 

 surface of the head, as is seen in the gad-flies (Tabanida?) (Fig. 226) ; 

 usually they are situated on the surface of the head, sometimes they 

 stand out prominently as in the praying mantis (Fig. 734), but occasion- 

 ally they are perched on long stalks (Figs. 228 and 229). Exceptionally 

 two compound eyes are differentiated in function, such as in the 

 whirligig beetle, Dineutus, which has a dorsal compound eye for aerial 

 vision and a ventral for vision under water (Fig. 231).- A unique organ 

 is seen in the Aphid family (" green-fly ") in which an additional tri- 

 faceted organ, the triommatidion, is found at the base of each 

 compound eye (Fig. 230) ; the function of this organ is imknown but 

 it is present even in those forms of aphids which have no compound 

 eyes. 



von Buddenbrock, Moller-Racke and 



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(1913). 

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253 (1930). 

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9 (1939). 

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Zool. Physiol., 31, 519 (1912). 

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(1942) ; 22, 115 (1943).' 

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(1956). 

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Leipzig (1891). 

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(1880). 

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 Hamilton. 



(1925). 

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(1926). 

 Harris and Mason 



280 (1956). 



, 18, 280 (1895). 



Publ. U.S. nat. Mus., 65, 1 



Lunds I 



Aarssr, 22 

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1 p. 172. 



Hentsfhel. Zool. Jb., Abt. Anat., 12, 509 



(1899). 

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Jena, 79 (1912). 

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Das Sehen der niederen Tiere, Jena 



(1908). 

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(1666-1699), 10, 609 (1730). 

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7, 201 (1928) ; 14, 40 (1931). 

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345 (1952). 

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(1935). 

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20,84(1945). 

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d. Wirbellosen Tiere, Jena, 664 (1893). 

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(1905). 

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Sci., 23, 177 (1883). 

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Zool. Jb., Abt. Anat. ,2,1, -m, 281 (1909). 

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5, 49 (1891). 

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 sinnes des Mensclien it. d. Thiere, 



Leipzig (1826). 



Dragon-fly 



Whirligig beetle 



Aphid 



- Compare the eye of Anableps, p. 324. 



S.O. — VOL. I. 



15 



