CASSIOPEA XAMACHxVNA. 223 



not so contracted show at lei^t tlie deeper part of the cavity, whieli theret'on*, nmy be 

 truly a vestige of the septal funnel. 



At an early stage of strohilization there may be noticed a sliort conical projection 

 from the central edge of each coluniellii. It extends also around the sides. These pro- 

 jections are pri>bal)ly the rudinuMits of the first four gastric (ilanients, which are dis- 

 tinctly developed at liie time wiicn the ephyrida is set fi'ce (j//, Fig. -58). 



While the sept:i are shiinkiiig to Itecome tiie coUiinellae, ridges appear opposite 

 eacli otiier on the upper ami lower wails of the peripheral part of the digestive tract 

 between the bases of the tentacles. The epithelial membranes at the summits of op[)0- 

 site ridges unite, and thus there is formed a series of lines of adhesion extending inward 

 from the jieriphery and dividing the sjjace into a series of radial canals, each ending in 

 a tentacle. Tlie two discs of mesogloea never fuse along these lines of adhesion, but the 

 endoderm remains lietween them as the endodermal lamella, or cathanimal plate. At the 

 stage of Fig. 2i the lines of adhesiim occupy abcnit half the space from the margin to 

 the cohuncllae. 



The lower disc ol I he slrobila ri'nuiins simply an a,niiular fold of the body wall ind.il the 

 metamor[)Iiosis of the upper disc is nearly complete. The se[ital muscles in this region 

 bend outward with the rest of the body wall (Fig. 57) . At length, however, the endoderm 

 grows out toward the periphery as four shallow pouches, leaving septa, between them 

 which contain the longitudinal muscles. Very soon after this the septa are perforated so 

 as to allow a fusion of the endoderm at their upper angles (Fig. 58). In the last stage 

 of strohilization (Figs. 2li and O'J) the longitmlinal muscles may be traced from the 

 peristome thronnh the columellae and the mesoycloea. of the exumbrella. to the narrow 

 isthmus wluue the ephyrula disc joins the basal [)olyp. The latter has now a well- 

 deseloped peristome (Fig. -VJ), and the mesogloea iu this region is very thin. Just in 

 tlie istlnnus the muscles have ilisap[ieared, but. they may be found again in the [)eristome 

 of the basal polyp and traced for a distance close under the epithelium to tlie edges of 

 the se[>ta, where they lieud abruptly downwaid, and continue through the septa, into the 

 stem. 



Altlnnigh seldom \isible in the living specimen, sections sIkjw that tlie basal polyp 

 at this stage possesses eight short tenacles (Fig. 5!)). It has al.so an annular fold of the 

 ectoderm, closely surrounding the isthmus (Fig. 51) and^/. Fig. 611). This fold is the 

 rudiment of a new [iroboscis, which is without doubt, entirely ectodermal in origin. But, 

 as Goette has pointed out, it does not follow from this that the lining of the [iroboscis is 

 ectodermal in scy|ihislomas developed from the egg. Pulsating contractions of the 

 umbrella, are lirst noticed at the time when the rhopalial tentacles begin to be ab.sorbed 

 (Fig. 21). They are then feeble and at long intervals. At the stage of Fig- 2G these 



