ON CTENOPLANA. 3993 
tions of the Ctenophores, namely, that of Chun! and that of 
Lang.? These may be briefly tabulated as follows. 
According to Chun— 
1. Tentacle or funnel-plane of Ctenophores = Sagittal plane of Bilateralia. 
. Stomachal plane of Ctenophores = Transverse plane of Bilateralia. 
3. Main axis of Ctenophores*® = Longitudinalaxis of Bilateralia. 
[a 
According to Lang— 
1. Tentacle or funnel-plane of Ctenophores = Transverse plane of Polyclades. 
. Stomachal plane of Ctenophores = Sagittal plane of Polyclades. 
3. Main axis of Ctenophores becomes bent (geknicht) in Polyclades. 
tw 
From the above it will be seen that, as regards the tentacle and 
stomachal planes, Lang’s interetation is the exact reverse of 
that of Chun; and yet it is singular that there is no mention 
of such a fundamental discrepancy in Lang’s monograph. 
Selenka (quoted by Lang) held the view that the anterior 
end of a Polyclade corresponded to the aboral pole of the 
Ctenophore, and the posterior end of the former to the oral 
pole of the latter. Lang says he himself formerly held this 
view, but afterwards gave it up as being erroneous. It would, 
however, necessarily follow if the main axis of the Ctenophores 
corresponded to the long axis of Polyclades as stated by Chun. 
The latter view, however, is irreconcilable with Chun’s own 
identification of the tentacle plane of Ctenophores with the 
sagittal plane of Bilateralia, and, in fact, it may be dismissed, 
once for all, as erroneous. 
Chun’s other homologies, however, in respect of the tentacle* 
and stomachal planes are fully confirmed by the conditions 
1 Carl Chun, ‘ Die Ctenophoren des Golfes von Neapel,’ 1880. 
2 Arnold Lang, ‘ Die Polycladen des Golfes von Neapel,’ 1884. 
3 Carl Chun, “Die Verwandtschaftsbeziehungen zwischen Wiirmern und 
Ceelenteraten,” ‘ Biol. Centralblatt,’ Bd. ii, 1882-8. In this paper Chun 
intimates that the main axis of Ctenophores becomes the long axis of Poly- 
clades; but I cannot find out how he reconciles some of the views here 
expressed with the previous statements as to the homologies of the planes 
contained in his monograph. 
4 Chun denominated the plane in which the tentacles of Ctenopkora lie 
the Trichterebene, because there are no tentacles in the Beroide. 
