42 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



The method of ascertaining whether this sense 

 is lodged in the marginal bodies was, of course, 

 extremely simple. Choosing a dozen of the most 

 vigorous specimens, I removed all the marginal 

 bodies from nine, and placed these, together with 

 the three unmutilated ones, in another bell-jar. 

 After a few minutes the mutilated animals recovered 

 ii'om their nervous shock, and began to swim about 

 with toleiable vigour. I now darkened the room, 

 and threw the concentrated beam of light into the 

 water as before. The difference in the behaviour 

 of the mutilated and of the unmutilated specimens 

 was very marked. The three individuals which 

 still had their marginal bodies sought the light as 

 before, while the nine without their marginal bodies 

 swam hither and thither, without paying it any 

 I'egard. 



A further question, however, still remained to be 

 determined. The pigment spot of the marginal 

 body in Medusae is, as L. Agassiz observed, placed in 

 front of the presumably nervous tissue, and for 

 this reason he naturally enough suggested that if 

 the marginal body has a visual function to perform, 

 the probability is that the rays by which the organ 

 is affected are the heat- rays lying beyond the range 

 of the visible spectrum. Accordingly I brought a 

 heated iron, just ceasing to be red, close against the 

 large bell-jar which contained the numerous speci- 

 mens of Sarsia ; but not one of the latter approached 

 the heated metal. 



From these observations, therefore, I conclude 

 that in Sarsia the faculty of appreciating luminous 



