CTENOPHORA. 63 



The stoniodaeum is seen in a very marked way to consist of two distinct parts. The upper 

 part is strongly compressed in the sagittal plane; its rather thick walls curve outwards above at the 

 opening into the infundibulum, as a pair of inner lips. This part is distinguished as the oesophagus. 

 Between the oesophagus and the pharyngeal vessel is a conspicuous clear space, without muscles, 

 which may be distinguished as the diaphragm, as it is doubtless the homologue of the diaphragm 

 in the Polyclads. Below the oesophagus the stomodaeum is not compressed in the sagittal plane. It 

 is nearly square, a little larger in the transverse plane. This, evidently, depends on the strong devel- 

 opment of the pharyngeal folds. There is a distinct keel on each side in the sagittal plane, but it is 

 only farther down that the sagittal compression of the stomodeeum becomes apparent. This lower, 

 larger part of the stomodseum, comprising the stomodaeal folds, is distinguished as the pharynx. — 

 This differentiation of the stomodaeum, which has hitherto been overlooked, as it appears, is a 

 general feature in the Ctenophores. I have foimd it quite easily observable also in Pleurobrachia, 

 (comp. fig. 13, p. 70) Euchlora and Bolina, besides in Tjalfiella and upon the whole in the Platy- 

 ctenida; also in Beroe it exists. Likewise the same feature is found in the Polyclads. (Comp. above, 

 p. 53). It is especially distinct, where the pharyngeal folds are much developed, causing thus a 

 widening of the pharynx in the transverse plane; where the folds are only small, the pharynx is 

 compressed in the sagittal plane also in the upper part, so that the transition from the pharynx 

 to the oesophagus becomes quite even, no distinct limit being seen. 



The pharyngeal folds are, as seen in fig. 11, strongly developed, in the shape of the usual 

 folded bands. In Mertens' figure i, Taf. 9, they are very well shown; he describes them (designating 

 them as "Gallengefasse") as "ganz driisigte gewundene Organe, die bis an die Mundspitze reichen, 

 und dort noch nach aussen gegen sich selbst eingeschlageu sind". Moser's statement (p. 124) that 

 "liber Form und Lange der Magenwiilsten fehlen bisher Angaben" thus does not hold good — and even 

 in case the Beroe compressa of Mertens were really different from M.ovum, that statement is not 

 correct Fabricius says in his description of "Beroe ovum" (Fauna groenlandica, p. 362): "Intra illos 

 cirros (the tentacles), et paulo anterius, 2 cirri minores rubicundi conspiciuntur, quos extra corpus ex- 

 tendere non vidi, nee credo illam posse". It appears evident that these two short "cirri" can only be 

 the pharyngeal folds; this is put beyond doubt by the following notes found (on p. 288) in a hand- 

 written work of O. Fabricius: "Zoologiske Samlinger eller Dyrebeskrivelser" (1809), preserved in the 

 Zoological Museum of Copenhagen; they are given here in translation. "The two shorter cirri, which 

 have their place between the long ones in the middle of the worm (as it appears, in the cavity itself), 

 were pink brown, and must be regarded as a pair of mouth-tentacles. . . . When it has got the Crustacean 

 ("Marfluen", "C«zj«^.y«V««/«") agglutinated with its cirri and carried to the mouth, the Crustacean appears 

 to become powerless, and the mouth tentacles then catch it there and carry it further to the 

 stomach". — Fabricius thus has not only observed and described the pharyngeal folds of M.ovut?i 

 long before Mertens, but he is, upon the whole, the first, who has seen this structitre of the 

 Ctenophores. 



Regarding the gastrovascular system I cannot give any information beyond that given above 

 of the position of the pharyngeal vessels. I would only recall the remarkable statement of Mertens 

 (Op. cit. p. 526), that from the part of the subtransversal vessels continuing towards the apical pole 



