REPORT ON THE DEEP-SEA MEDUSAE. 75 



becomes considerably thickened above, and then passes directly into the four perradial 

 palatine nodes (gk), by which the buccal stomach is fixed to the subumbrella. 



The palate or palatine opening ("palatum, porta palatum," #p ; PI. XX. fig. 11 ; PI. XXI. 

 figs. 12, 13, 18, gp) forms the important opening for communication between the buccal 

 stomach (ga) and central stomach (gc) ; it can probably be completely closed by muscular 

 contraction in the living Periphylla. Properly speaking, it consists of the wide central 

 palatine opening and the four perradial palatine grooves surrounding it. The central 

 palatine opening (" porta palatina", gp) is quadrate, its interradial lateral margins are 

 formed by the upper, swollen and thickened, aboral margins of the buccal columns (ac), 

 which here pass immediately into the lower delicate oral margins of the thin obelisk 

 plates (gz). Its perradial corners, on the other hand, communicate by a narrow cleft 

 (perhaps capable of closing) with the four palatine grooves which represent in some 

 measure four secondary openings of the central principal opening (figs. 8, 11, 18, ga). 

 These four perradial palatine grooves (" sulci palatini," gs) lead from the oral cavity 

 immediately towards the outside into the coronal sinus, and form, at the same time the 

 dilated distal ends of the cleft-shaped gastral openings (go). They are imbedded in the 

 cartilaginous mass of the four palatine nodes (" nodi palatini," gh). It appears that the 

 palatine grooves remain open even when the principal opening is completely closed, 

 and then by contact of the two lips of their fissure can be transformed into short closed 

 canals (of about 3 mm. in diameter). 



The central stomach (" gaster centralis, obelisk stomach," gc ; PI. XX. fig. 8 ; PI. 

 XXI. figs. 11-18), the middle of the three divisions of the axial principal intestine, is 

 somewhat smaller than the buccal stomach, and has, on the whole, the form of an obelisk 

 or a truncated regularly quadrilateral pyramid (figs. 12, 13, gc). We can distinguish 

 geometrically two bases and four lateral surfaces. The lower (oral) base is formed by the 

 palatine opening described above (" palatum," gp), by which the central stomach opens 

 into the buccal stomach. The upper (aboral) basis, on the other hand, occupies the 

 quadratic pyloric opening (" pylorus" gy), by which the central stomach communicates 

 with the basal stomach. The four interradial lateral surfaces of the obelisk-shaped central 

 stomach form four trapezoid, or almost rectangular thin lamellae, which on account of their 

 special importance I have termed (once for all, to prevent confusion) the four obelisk plates 

 of the central stomach (" tabulae obelisci," gz). The thin wall of these quadrangular plates, 

 which are placed more or less vertically, belongs properly to the subumbrella, and is 

 formed by a delicate but firm gelatinous plate or supporting lamella, whose inner or 

 axial surface is covered by gastral endoderm and its outer or abaxial surface by the 

 subumbral ectoderm of the funnel cavities, and a thin layer of muscle belonging to it. 

 The upper or aboral margin of each obelisk plate is formed by a quadrant of the pyloric 

 stricture (gy), the lower or aboral margin by a quadrant of the palatine stricture (gp), 

 whilst the two lateral or longitudinal margins are beset with a row of gastral filaments 



