CASSIOI'KA \\M\CIIANA. 223 



not so contracted show at least the deeper part of the cavity, whicli therefore, ni:i,y be 

 truly a vestige of the septal funnel. 



At an early stage of strobilization there may be noticed a short conical projection 

 from the central edge of each colnmella. 1 1 extends also around the sides. These pro- 

 jections arc probably the rudiments of the (irst four gastric filaments, which are dis- 

 tinctly developed. at the time when the ephvrula is set free ('//', Fig. 58) . 



While the septa are shrinking to become the columellae, ridges appear opposite 

 each other on the upper and lower walls of the peripheral part of the digestive tract 

 between the bases of the tentacles. The epithelial membranes at the summits of oppo- 

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

 from the periphery and dividing the space into a series of radial canals, each ending in 

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

 endoderm remains between them as the endodermal lamella, or cathammal plate. At the 

 stage of Fig. 24 the lines of adhesion occupy about half the space from the margin to 

 the columellae. 



The lower disc of the strobila remains simply an annular fold of the body wall until the 

 metamorphosis of the upper disc is nearly complete. The septa,! 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 

 whicli contain the longitudinal muscles. Very soon alter 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 strobilization (Figs. 20 and 5'J) the longitudinal muscles may be traced from the 

 peristome through the columellae and the mesogloea of the exumbrella to the narrow 

 isthmus where (lie ephyrula disc joins the basal polyp. The latter has now a well- 

 developed peristome ( Fig. 5!l), and the mesogloea in this region is very thin. Just in 

 the isthmus the muscles have disappeared, but they may be found again in the peristome 

 of the basal polyp and traced fora distance close under the epithelium to the edges of 

 the septa, where they bend abruptly downward, and continue through the septa into the 

 stem. 



Although seldom visible in the living specimen, sections show that the basal polyp 

 at this stage possesses eight short tenacles (Fig. 5!>). It, lias also an annular fold of the 

 ectoderm, closely surrounding the isthmus (Fig. 5'J and p. Fig. GO) . This fold is the 

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

 as Goette has pointed out, if does not follow from this that the lining of the proboscis is 

 ectodermal in sc.yphistoma.s developed from the egg. Pulsating contractions of the 

 umbrella are first noticed at the time when the rhopalial tentacles begin to be absorbed 

 (Fig. 24). They are then feeble and at long intervals. At the stage of Fig. 26 these 



