REPORT ON THE DEEP-SEA MEDUSAE. lxxv 



§ 109. The three chambers of the principal intestine ("gaster principalis"). The 

 central 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," fig. I, go), 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," gc). The third or uppermost section is the peduncle tube or 

 basal stomach (" gaster basalis," gb), which ends caacally at the aboral pole of the principal 

 axis. The central stomach communicates with the basal stomach, below by the palatine 

 opening (" porta palatina," gp), above by the pyloric opening (" porta pylorica," gy) ; 

 besides these there are usually gastral openings (" ostia gastralis," go), in the lateral 

 walls of the central stomach, by which the latter communicates with the radial chambers 

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

 both sections (namely Anthomedusae and Peromedusae) ; the uppermost (basal) stomach 

 has, however, usually undergone retrograde formation. In the majority of Medusas, 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. All the three chambers can 

 be already distinguished in many polyps (both Hydropolyps and Scyphopolyps). The 

 buccal stomach of the Medusae corresponds to the freely projecting proboscis (" tubus 

 oralis ") of the polyps, the central stomach to their peculiar " calyx stomach " (" cavitas 

 calycina "), and the basal stomach to their peduncle tube (" tubus peduncularis "). 



§ 110. Buccal stomach or oesophagus ("gaster buccahs," also termed "tubus oralis, 

 proboscis, manubrium," go). The buccal stomach or oesophagus (go) is the first and 

 lowest of the three chambers of the principal intestine. It is evolved from the 

 "oesophagus" or "proboscis" of the polyps, and shows extraordinary diversity of size, 

 form, and differentiation. It originally bears the oral opening (aa) at the oral pole of its 

 vertical axis, whilst it opens at the aboral pole of the axis into the central stomach (gc) 

 by the palatine opening (gp) ; the latter is sometimes sharply defined, sometimes 

 indistinct. The palatine opening is usually found in the middle of the subumbrella, so 

 that the oesophagus hangs freely from the latter into the umbrella cavity. In the 

 majority of the Medusae, the oesophagus is the longest, but not the broadest of the three 

 gastral chambers. It is developed exceptionally strongly in the Anthomedusae, Tracho- 

 medusae, Peromedusae, and Discomedusae, whilst in the other orders it is usually weak 

 or often quite rudimentary. The oesophagus rarely forms a simple cylinder without 

 radial division (as in the Codonidas, System, taf. i., ii. ; and in many Narcomedusae, 

 System, taf. xix. xx.). In the majority of Craspedotae, and in all Acraspedae, the 

 oesophagus is prominently quadrilocular, as the four perradial buccal ribs (" costae 

 orales," ab) have a tendency to centrifugal growth, project towards the outside, and 

 become prolonged into the midribs of the oral lobes, whilst the four intermediate buccal 



