350 PHYSIOLOGY OF THE INVERTEBRATA. 



this mass dashed themselves against the glass nearest the 

 light with a vigour and determination closely resembling the 

 behaviour of moths under similar circumstances. There can 

 thus be no doubt about Sarsia possessing a visual sense." 



To prove that the ocular spots of these animals are really 

 eyes, Dr. Romanes experimented in a like manner with a 

 dozen vigorous specimens ; nine of which had previously had 

 their ocular spots removed, while three specimens were left 

 intact. The difference in the behaviour of the mutilated and 

 the unmutilated individuals was very marked. The three 

 unmutilated individuals sought the light as before, while the 

 nine blind or mutilated individuals swam hither and thither 

 without paying it any regard. 



It was suggested by Professor L. Agassiz, that it was the 

 heat, or ultra-red rays of the spectrum, which was the real 

 cause of the above phenomenon, but Dr. Komanes has shown 

 that when a heated piece of iron (" just ceasing to be red ") 

 was placed against the bell-jar containing the specimens of 

 tarsia, not one of the organisms approached the heated metal. 

 These investigations prove that in Sarsia the faculty of 

 appreciating luminous (but not heat) rays is present, and 

 that this faculty is lodged exclusively in the ocular spots. 



Dr. llomanes has also shown that the lithocysts of the 

 covered-eyed Mcduscc resemble, in function, the marginal 

 bodies of the naked-eyed Medusa' — that is, they are rudi- 

 mentary or incipient organs of vision. The lithocysts are 

 stimulated by the approach of a candle or the access of day- 

 light, but if the lithocysts are removed, the approach of a 

 luminous object produces no stimulating effect. 



The ocular spots in the Adinozoa, and especially in 

 Actinia mcscmhrT/anfheviirm, have been investigated by 

 Schneider, Eotteken, Duncan, and MacMunn. These 

 coloured bodies are situated in the oral disc outside the 

 tentacula ; and they are diverticula of the body wall. Be- 

 neath the surface " lies a layer of strongly refracting 

 spherules, followed by another layer of no less strongly 



