154 CEYLON PEAEL OYSTEE EEPOET. 



Description of the Peronia. It is in the perradii, without the tentacles, that the 

 appearance of a double canal is best seen, and transverse section in this position 

 shows the " septum" but no canals (fig. 1). 



In the two perradii, which have the tentacles, there is a longitudinal groove, the 

 peronial groove, running from the margin of the umbrella up to the tentacle. This 

 groove is very deep, running back to the wall of the sub-umbrella, cutting the wall of 

 the sub-umbrella nearly in two (fig. 2). At the bottom of this groove is the 

 peronial band (figs. 2 and 6), which runs from the margin of the umbrella to the 

 base of the tentacle. The peronial band is a solid cord of ectoderm cells, nearly 

 circular in transverse section, and surrounded by mesogloea, except on the side facing 

 the peronial groove. In the lower wall of the stomach there are two little funnel- 

 shaped pockets, one under the root of each tentacle. Sections show that the ectoderm 

 of the lower wall of the stomach, at the apex of the pocket, unites with the peronial 

 band, and is continuous with the ectoderm of the tentacle. In the ectoderm of the 

 tentacles there are large round nematocysts. These nematocysts form a conspicuous 

 band along the under or lower side of the tentacle near its base (fig. 6) and then, a 

 little further along, spread all round the tentacle. I have found similar nematocysts 

 in the ectoderm of the pockets in the lower wall of the stomach and scattered among 

 the generative cells (fig. 2) adjacent to the pockets. They are also in the strand of 

 ectoderm between the apex of the pocket and the tentacle, but not in the peronial 

 band, which is between this point and the margin of the umbrella. It seems to me 

 that the nematocysts develop in the lower wall of the stomach in the neighbourhood 

 of the pockets, then migrate into the ectoderm of the pocket and pass along the 

 strand to the ectoderm of the tentacle. 



The "septum" in the perradii, without tentacles, has the same structure as the 

 peronial bands connected with the tentacles, but there is no peronial groove and the 

 band (" septum ") is completely surrounded with mesoglcea. It starts from the 

 margin of the umbrella, runs up the side of the wall of the sub-umbrella, and at the 

 level of the lower wall of the stomach it curves outwards and passes through the 

 jelly to the ex-umbrella. In its passage through the jelly it tapers out almost to a 

 point, and in some specimens stops a little way short of the ex-umbrella. Its presence 

 marks the former existence of a tentacle, and shows that Solmundella is descended 

 from a medusa which had four perradial tentacles. 



The appearance of radial canals on each side of a " septum " is, in my opinion, due 

 to the transparent mesoglcea in the short interval between the gastric pouches. 



Sections across the margin of the umbrella do not show the existence of a definite 

 circular canal. 



Gonads. Some of the specimens have the gonads confined to the inner wall of the 

 gastric pouches, where they lie in the ectoderm (figs. 1 and 2). The gonads may 

 extend over the lower half of each gastric pouch or over the whole pouch. Some 

 of the large specimens have the gonads not only over the gastric pouches but 



