ARTHROPODA 



221 



forms which are unprovided with compound eyes — the primitive 

 wingless Collembola (Fig. 223), hce and parasitic fleas which possess 

 only ocelli (Fig. 224), while species which live in darkness may be 

 iniprovided with eyes, such as the Protura, the driver ant of Africa, 

 Dorylus (with the exception of the winged male), or most termites. 

 The winged male Stylops has aggregate eyes composed of a multitude of 

 ocelli so closely packed together as to resemble a compound eye, but 

 the parasitic female Mhich passes its whole life within its host, is 

 unprovided with eyes.^ 



jVIale driver ant 



Figs. 22.3 and 224. — Insects with Ocelli and Xo Compound Eyes 

 (Xatural History Museum, London). 







Fig. 2l':;. Tlic springtail, 

 Arrhi.stoiuti brs-selsi (Collem- 

 bola). 



There are 8 ocelli on each side 

 and no compound eyes. 



Fig. 224. — The bird-louse, Trinoton acidenlioii 

 (Anoplura). 



There are 2 simple eyes (S) on each side and no 

 compoimd eyes. 



We shall see ^ that the compound eyes are the dominant organs in the 

 adult insect, the simple eyes essentially accessory ; this is .seen in the occasional 

 disappearance of the latter as the former develop. Thus the larva of the 

 water-beetle, Dytiscus, has 6 ocelli on each side of the head, but in the later 

 stages of larval development the compound eye appears in front of them, first 

 as a crescentic area on each side. At the stage of moulting the cornea^ of the 

 ocelli are shed with the cuticle and as the compound eye rapidly develojDs the 

 bodies of the ocelli recede, remaining, however, permanently attached in vestigial 

 form to the optic nerves, 



1 For the descriptive anatomy of the compound eyes of Insects, see p. 166 ; for 

 that of the ocelli, see Hesse (1901), Merton (1905), Link (1908-9), Strohm (1910), 

 Demoll and Scheurins (1912). Bugnion and Poiwff ( 1914), Melin (1923). Homann (1924), 

 Hamihon (1925), Zikan (1929), Wolsky (1930-31), Friederichs (1931). Verrier (1940), 

 Lhoste (1941). 



^ p. 224. 



Female driver ant 



Stylops 



