114 EMBRYOLOGY 



scyphopolyp, aiid subsequently go through the process of 

 strobilization again, and so on. 



In most cases, however, new transverse furrows make 

 their appearance on the basal part before the detachment of 

 the first Ephyra, so that on the elongated cup of the scj^pho- 

 polyp a whole set of Ephyra? (ten to thirty) are developed at 

 approximately the same time ; but of these any one that is 

 nearer to the base of the polyp is younger than those distal 

 to it (polydisc stroh'da) (Figs. 56 and 51 e — lo). In this case 

 also the basal portion finally reproduces both a circle of 

 tentacles and the oral part of a scyphopolyp, and is thus 

 enabled to continue its existence as a scyphopolj^p when 

 the production of Ephyrte ceases. A polydisc strobila can 

 be derived from a monodisc. In the former new transverse 

 divisions follow one another so rapidly that a large number 

 of Ephyrfe are in process of development at the same time. 



The oral portion of a scyphopolyp, in metamorphosing 

 into an Ephyra, must undergo certain changes, part of 

 which make their appearance before the first indication of an 

 abstriction is produced by the circular furrow. The most 

 important internal change is introduced by the disappearance 

 of the septa and the peripheral communication between the 

 four gastral pouches which is thus brought about. Since 

 the entodermal columns of the four septal tentacles are con- 

 tinuous with the walls of both the gastral pouches adjoining 

 the septum (p. Ill), there is produced at this place a con- 

 nection between the neighbouring gasti-al pouches. At this 

 point a small perforation now arises in the septum (Fig. 54 

 so), but this very soon widens to such an extent that only 

 the thickened inner margin of the septum, which is tra- 

 versed by the septal infundibulum, is pi'eserved (Fig. 57 

 so). By the formation of these septal ostta, the four gastral 

 pouches coalesce into a common peripheral gastral chamber 

 (peripheral intestine) \_Kra7izdarm']. The four septal infundi- 

 bula, clothed by an entodermal covering (remains of the 

 septa), now traverse the gastral space in the form of four 

 columns (columella'), which are not attached to the wall of 

 the central stomach except at its bottom. 



A further change is brought about by the disappearance 



