STROBILIZATION OF AURELIA 95 



polyp does not arise in exactly the same manner as in the 

 ephyra. It occurs in the same relative position but apparently 

 not as a pit. A specimen showing the earliest trace had a solid 

 strand of cells reaching from the oral disc obliquely inwards 

 and downwards to the longitudinal muscle (PL 6, fig. 2, B.). At 

 the outer end was a slight depression which was probably the 

 commencement of the formation of a cavity in the strand. 

 Another specimen showed a complete pit the apex of which 

 bore the same relation to the longitudinal muscle as does that 

 of an ephyra (see Text-fig. 3). Probably, then, the strand of 

 cells becomes hollow from outside inwards. This cavity should 

 not be confused with that in the longitudinal muscle, nor do 

 the two ever communicate. 



Ciliation of the Ectoderm. — Gemmill (5) has shown 

 that, in the ephyra, there are definite currents passing over 

 the ectodermal surface apparently for the purpose of carrying 

 small animals to the lappets, where they are pierced by stingino- 

 threads and afterwards carried to the mouth by flexure of the 

 arm. He also states that the scyphistoma captures infusoria 

 in much the same way as the ephyra, the tentacles takino- the 

 place of the arm lappets. 



Powdered carmine suspended in sea-water will also serve 

 admirably to demonstrate these currents. In the scyphistoma 

 the carmine particles are carried upwards along the surface of the 

 body and become entangled in shme secreted by the ectoderm. 

 Between the bases of the tentacles ropes of particles and slime 

 may be seen carried along the disc and up to the edge of the 

 proboscis. The tentacles, along which the current passes to 

 the tip, sometimes curl over into the proboscis and the material 

 travels into the gastric cavity. Often a slowly revolving ball 

 is formed above the mouth and finally passes slowly down into 

 the enteron. The same applies to the ephyra, in which the 

 passage of the carmine ball into the gastric cavity can be easily 

 seen. Sometimes the ball will be slowly ejected from the 

 enteron immediately after being taken. Gemmill beheves that 

 particles are taken in ' by a central inhalant current which is 

 compensatory to exhalant currents produced by ciliary action 



