STROBILIZATION OF AURELIA 93 



muscle here is degenerate, and the apical portion of the ephyra 

 is thickened with mesogloea in which the muscle remnants 

 can be seen (fig. 5, L.M.). As Heric suggests, the separation is 

 probably brought about by the violent action of the circular 

 and radial muscle-bands. The connecting strands break close 

 to the exumbrella. About the same time the stretched part of 

 the columella breaks, resulting in the carriage of the gastral 

 filaments to the subumbral side. The remnant of the stretched 

 portion is seen as a small papilla of cells between the bases of 

 the gastral filaments (PI. 6, fig. 3, B..C.). 



The rupture of the columella brings about a rapid shortening 

 of the peristomial pit, which is now seen to be a small but 

 distinct funnel-shaped depression (fig. 3, P.P.) in the sub- 

 umbrella close to the bases of the gastral filaments. The greater 

 part of the wall of the pit has gone to form a portion of the 

 subumbral surface and the base of the manubrium. The pit, 

 which was close to the base of the manubrium, is now some 

 distance away. The gastral filaments no longer point to the 

 oral opening but come to be roughly in a line at right angles 

 to the interradius. 



When an ephyra becomes free the connecting strands are left 

 projecting from the oral opening of the next ephyra (PI. 6, 

 fig. 10, C.S.) and are soon reduced in length. The flat manu- 

 brium of this next disc now begins to assume the tubular form, 

 which is not completed until separation- and the rupture of the 

 columella (PI. 6, fig. 5). 



Muscle remnants are to be found in a newly separated ephyra 

 in the thickened apex (PI. 6, fig. 4) and at the base of the manu- 

 brium on the inner side of the peristomial pit. A vestige of 

 the connecting strand and the part of the muscle between it 

 and the apex of the pit can be found at the base of the manu- 

 brium (PI. 6, fig. 3, R.L.M.). 



Formation of the Proboscis of the Polyp . — 

 A strobila can be divided into two regions, viz. segmented, 

 giving rise to ephyrae, and unsegmented, producing the 

 polyp. Between every two adjacent constrictions lie four 

 septal ostia arranged in a ' ring-sinus '. Below the lowest 



