WORMS. 



135 



rig. 89 represents an eye-dot of Nereis. In tbis 

 jenus there are two pairs of eyes, which differ some- 



Fig. 88. — ^terior extremity of a freshwater worm {Bohemilla comata) ; after 

 Vejdo'vsky).* a, Eye; b, braia, c, cuticle; Ap, liypoilerm; Iby tactile hair; 

 ne, nerve , «, blood-vessel. 



what in structure, the lens in the anterior pair being 

 flatter, that in the posterior more conical. In Hesione 

 the diflference is even more 

 marked.f In Polyophthalmus, 

 besides the eyes in the head, 

 there is, as already mentioned, 

 a series along the sides of 

 the body, which differ some- 

 what in structure from those 

 in the head. 



As a general rule, in the Annelids each eye contains 

 a single lens, but the cephalic eyes of Polyophthalmus, 

 according to Mayer, contain three. 



* " Sys. imd Morph. der Oligochseten." 



t Graber, " Morph. Unt. iiber die Augen der frei-lebenden BorsteD- 

 wiirmer," ArcJi fur Mic. Anat, 1880. 



Fig. 89. — Eye-dot of Nereis (after 

 Miiller). In B the pigment is 

 partly removed so as to show 

 the lens. 



