1914] Lifik: OccUi of I'oliiorchis 311 



fitC. 3) and thus stand out more proniiiK'ntly and their basal 

 tentacular bulbs are also larger. 



"When the animal is resting quietly at the surface of the water 

 and fully relaxed, the tentacles may become extended to twice the 

 length of the bell. They are very sensitive to touch and, when 

 slightly disturbed, and often apparently for unknown causes, 

 the tentacles contract, either singly or all at once to much less 

 than the length they attain when relaxed. If suddenly or forcibly 

 disturbed the animal sharply contracts the velum, constricting 

 the bottom of the bell till it becomes at times almost globular. 

 The tentacles are then folded inward and contracted until only 

 short thick stubs are seen. This is the condition often assumed 

 in death or upon treatment with tixing agents. 



The animal moves about by quick jerky contractions of the 

 velum and bell muscles— those along the four radial canals being 

 most apparent— so that the space within the inner bell surround- 

 ing the manubrium is suddenly diminished. The water thus 

 forced out the opening in the velum gives a push to the bell that 

 impels the animal forcibly in the apical direction, much after 

 the manner of a squid when water is forced out of its siphon. 



All medusae have marginal bodies situated on the rim of the 

 bell, though their number, structure, and position are variable. 

 These marginal bodies may be either auditory, olfactory, or visual 

 in function. Only in very rare cases {Stmirostoma arctica) are 

 any two kinds of such bodies found on the same animal. It is 

 on this basis that the Hydromedusae are divided into Ocellata, 

 with eye-spots, and Vesiculata, with otocysts. The position of 

 the ocelli is sometimes directly on the rim but more often at the 

 base of the tentacles. In Lizzia these visual organs are found 

 on the underside of the tentacle, which is rather unusual. This 

 is related, however, to the fact that Lizzia holds the tentacle up 

 in a vertical direction and its lower side with its eye-spot is thus 

 turned toward the light. 



In Folyorchis we find an eye-spot or ocellus {oc, pi. 13, fig. 1, 

 pi. 14, fig. 3) on the outer surface at the base of each tentacle 

 where it leaves the rim of the bill. These purple eye-spots are 

 termed ocelli, since they are regarded as one of the primitive 

 types of eyes. At this .junction the tentacle becomes thickened to 



