132 



ECHINODEEMS. 



present; the eye, if so it can be called, in many species 

 consisting merely of a coloured spot, while in others 

 it is entirely absent.* 



Fig. 85.— Eye-spot of Lizzia (after 

 Hertwig). oc, Ocellus ; I, leus. 



Fig. 86. — Eye-bulb of Astropecten (alter 

 Haeckel). 



In the Echinoderms, the eyes, which were discovered 

 bv Ehrenberg, have been described by Haeckel,! 

 Wilson',1 Lange, and others.§ They ai'e in some cases 

 situated, as in Astropecten, on a pear-shaped bulb 

 (Fig. 86). 



They consist of a lens (Fig. 87), supplied with a 

 nerve, and lying in a mass of pigment. In Solaster or 



• AUman, "Mon. of the Hydroids," Ray Society, 1871. 

 t " Ueber die Augen und Nerven der Seesterne," Zeitfiir Wiss., vol. x. 

 X Transactions of the Linnean Society. 



§ Lange, "Beit. z. Anat. und Hist, der Asterien und Optiuren," 

 Morpli. Jahrhuch, 1876. 



