REPORT ON THE DEEP-SEA MEDUSAE. 73 



Peromedusse by many very peculiar and complicated arrangements, which can only be 

 completely understood after long and minute study. The only gastrovascular system 

 among the forms of the Medusae systems hitherto known, which offers more detailed 

 points of comparison, is that of the Lucernaridse, and in PervphyUa, as in the Lucernaridse, 

 it is derived from that of Tesseridse (comp. the general anatomical representation of the 

 Stauromedusse in my System, 1879, pp. 363-395, taf. xxi., xxii.). But whilst the 

 essential condition of the central gastrovascular system in those Stauromedusae 

 resembles that of the Perornedusse, in the Peromedusae it differs in detad in very import- 

 ant and peculiar complications, and especially in the formation of the peripheric part. 

 Generally speaking, we can distinguish in all Peromedusas two principal sections of the 

 gastrovascular system, the central principal intestine (" gaster principalis ") and the 

 peripheric coronal intestine (" gaster coronaris ") ; they are only connected by four 

 narrow, cleft-shaped, perradial gastral openings, and are otherwise completely separate. 



The central principal intestine (" gaster principalis ") occupies the entire length of the 

 axial space of the body and extends from the umbrella cone to the oral margin. It is 

 divided by two circular constrictions or horizontal strictures into three principal sections 

 — basal stomach (gb), central stomach (gc), and buccal stomach (ga). The upper or aboral 

 circular stricture between the basal and the central stomachs, I term the pyloric opening 

 or pylorus (" porta pylorica," gy) ; the lower or oral circular stricture, between the 

 central and the buccal stomachs, the palatine opening or palatum (" porta palatina," gj)). 

 In order to gain a general correct idea of the complicated conditions of form of these three 

 sections of the principal intestine, it is convenient to refer them to simple mathematical 

 figures ; the basal stomach is a cone (or more properly a epiadrate pyramid), the central 

 stomach an obelisk (or a truncated, regular quadrangular pyramid), the buccal stomach 

 a cube (or a four-sided prism) . The central stomach communicates with the peripheric 

 circular sinus of the coronal intestine by four lanceolate perradial openings (" ostia 

 gastralia "). 



The buccal stomach (eventually also termed proboscis or oesophagus, "gaster 

 buccalis, tubus oralis, proboscis " PL XIX. fig. 6 in the centre ; PI. XX. fig. 1 1 ; 

 PI. XXI. fig. 19) forms the lowest oral third of the axial principal intestine, is dice-shaped 

 on the whole, and hangs perfectly freely in the centre of the coronal hollow of the umbrella, 

 as it is only fastened above to the suburnbrella by the four perradial palatine nodes (cfk). 

 The length of the edge of the cube amounts to nearly 5 cm.; Plate XX. shows it apart 

 in its natural size, fig. 9 the interradial external view, fig. 10 the perradial external view, 

 and fig. 11 the perradial transverse section. The lower (oral) wall of the cube occupies 

 the quadrate oral opening (oa), and the upper (aboral) wall the palatine opening (gp) ; 

 the four perradial vertical lateral surfaces of the cube are formed by the buccal pouches 

 (bb), the four interradial edges between them by the buccal columns (ac). 



The oral opening (" osculum," cm), is shown from below in the middle of fig. 6 of 



(ZOOL. CHALL. EXP. — PART XII. — 1881.) M 10 



