MIDDLE CAMBRIAN. 27 



brevitj' we shall term tbe former the principal intestine and the latter the coronal 

 intestine. The central or principal intestine ("gaster principalis, axogaster") is simple 

 and undivided; its axis is at the same time the principal axis of the whole body; the 

 umbrella cone (or center of the gelatinous umbrella disk) lies at its aboral pole; the 

 oral opening at the oral pole. The peripheral or coronal intestine ("gaster corouaris, 

 perogaster"), on the other hand, is always divided by radial septa (or cathamma) into 

 four or more radial cavities (pouches or canals). The ideal circular or polygonal 

 boundary line between the principal intestine and the coronal intestine is consequently 

 defined by the proximal ends of the septa or cathamma; the gastral openings ("ostra 

 gastralia") lie between them. These narrow or wider fissures are the only openings by 

 which the central or principal intestine communicates with the divisions of the radially 

 divided coronal intestine. 1 



The central or principal intestine of the medusae is rarely perfectly simple ; it is 

 usually divided more or less distinctly into two or three sections or chambers, lying 

 one above the other in the principal axis of the body. The lowest of these is the 

 oesophagus or buccal stomach ("gaster buccalis"), which contains the oral opening at 

 the oral pole of the principal axis. The middle chamber is the principal cavity or 

 central stomach ("gaster centralis"). The third or uppermost section is the peduncle 

 tube or basal stomach ("gaster basalis"), which ends coecally at the aboral pole of the 

 principal axis. The central stomach communicates with the basal stomach — below 

 by the palatine opening ("porta palatina"); above by the pyloric opening ("porta 

 pylorica"). Besides these there are usually gastral openings ("ostia gastralis"), in 

 the lateral walls of the stomach, by which the latter communicates with the radiaj 

 chambers of the coronal intestine. All three stomachs are well developed in many 

 medusae of both sections (namely, Anthomedusae and Peromedusae); the uppermost 

 (basal) stomach has, however, usually undergone retrograde formation. In the majority 

 of medusae the buccal stomach is the longest, the central stomach the broadest of the 

 three chambers, whilst the basal stomach is the smallest, or has disappeared. 2 



The actual and theoretical information concerning' the g-astrovascnlar 

 system of this species that I have thus far secured is illustrated by text figs. 

 4, 5, 6, and 7 (pp. 28, 29). The general form of fig. 4 is restored from speci- 

 mens like those represented by figs. 1-4 of PI. I; the radial canals, figs. 1, 

 3, 4 of PI. Ill; oral arms, figs. 8, 8a of PI. II; central and buccal stomach, 

 figs. 8b of PI. II, 1 and 4 of PI. Ill, and 9, 10, 11 of PI. IV. It is not pos- 

 sible, owing to the condition of preservation of the inner parts of the medusas, 

 to determine the shape and size of the central intestinal tube or stomach. 

 That it was not simple in the typical form is fairly well shown by the 

 natural section, fig. 8b of PI. II. In the restoration (text figs. 4 and 5) the 

 central stomach may have been relatively broad in some specimens (figs. 



'Haeckel, loc. cit., p. xlviii, par. 99. 

 2 Haeckel, loc. cit., p. Ixxv, par. 109. 



