218 ROBERT PAYNE BIGELOW ON 



forty-two tentacles, from which the section represented in Fig. 51 was taken, this per- 

 foration was very small. Figs. 52 and 53 represent a little later stage, in which the 

 opening has become much wider. 



Each septal muscle is a solid cord of cells, with a single layer of longitudinal muscle 

 fibres in its periphery. In the peristome the fibres of the septal muscles spread out in a 

 fan-shaped arrangement toward the margin. 



Four slight interradial depressions in the peristome may be observed as early as the 

 four-tentacle stage. They are deeper in the eight- and sixteen-tentacle stages, and the 

 septal muscles may be seen to join the ectoderm at their bottoms. These depressions may 

 be homologous with the septal funnels of the Stauromedusae, or they may be merely the 

 result of the contracted condition of the larva. The question is of no importance, for 

 there can be no doubt about the homology of the muscles ; and whether they are solid or 

 hollow is merely a matter of detail. In later stages (Figs. 51 and 52) sections seem to 

 show that the peristomal depressions have deepened centrally so as to leave the inser- 

 tion of the septal muscles high up on the peripheral side. But here, again, before any 

 morphological conclusions can be drawn, account must be taken of the growth of the 

 perradial angles of the proboscis and of the effect of the contraction of the septal and 

 peristomal muscles. 



Relation of Septa to Interradial Tentacles. According to Goette, the interradial 

 tentacles are always interseptal in origin. That is, two of these tentacles are produced as 

 diverticulae from each of the second pair of gastric pouches (ectoderrnal) . and their subse- 

 quent position in the planes of the septa is due to a secondary shifting. He finds 

 in this important evidence in favor of his theory of the close affinity between the 

 Scyphomedusae and the Anthozoa, for the tentacles of the latter are also invariably inter- 

 septal. Glaus, on the other hand, finds that the interradial tentacles of Aurelia and Coty- 

 lorhiza are variable in origin. According to his observations ('91 and '92) , an interradial 

 tentacle may be interseptal, that is, arise as a diverticulum of a single gastric pouch, the 

 endoderm growing out and pushing the ectoderm before it ; or it may arise in the plane of 

 a septum by the union of two endodermal diverticulae, one from each of the adjacent 

 pouches. He holds, therefore, that the origin of the tentacles cannot be used as evidence 

 to uphold Goette's theory. 



My observations on Cassiopea are in perfect accord with those of Glaus. A number 

 of series of transverse serial sections made from young scyphistomas in the eight- and 

 sixteen-tentacle stages were studied carefully with the aid of camera sketches drawn on 

 transparent paper. By this means the relations of the parts could be determined accu- 

 rately ; and the results are embodied in the series of diagrams, Figs. H to L. In the 

 eight-tentacle stage, according to Goette, the gastric pouches in the long diameter, r r, 



