244 TRANSACTIONS OF THE [JUNE 5 
there is a loose fold of the integument continuous behind with 
the median raphe or keel of the tail. The cloacal aperture 
occurs at the end of a small papilla, which is often completely 
hidden beneath this loose fold on the right side of it. The 
cloacal papilla, however, undergoes varying degrees of con- 
crescence with the fold and, accordingly, sometimes the aper- 
ture lies quite near the extremity of the latter, but still some- 
what to the right of the middle line, as in Fig, 2. 
In one case only, out of the many that I examined, was the 
cloacal aperture placed on the mid-ventral line, as in Fig. 3. 
In another isolated instance, a very striking condition was 
observed (see Fig. 1). The hinder end of the above-mentioned 
loose integumentary fold was bifid, and presented at first sight, 
a perfectly symmetrical appearance. On close inspection, how- 
ever, it became evident that the left half of the fold was con- 
tinuous with what has been referred to above as the raphe or 
keel of the tail, while the right half hung freely and bore the 
cloacal aperture at its tip. 
Iam not aware that attention has ever been drawn to this 
asymmetrical position of the cloacal aperture in the Batrachian 
tadpole, nor to what extent it occurs in other species. It is 
certainly not universal. In the tadpoles of Bufo lentiginosus 
for instance, the external opening of the cloaca lies normally in 
the mid-ventral line, whereas, we have seen that in those of R. 
clamaia the asymmetrical position is the usual one, and the 
median position is the exception. 
Héron-Royer and Ch. van Bambeke, in their researches on 
‘“Le vestibule de la bouche chez les tétards des batraciens 
anoures d’ Kurope,” (Archives de Biologie IX., 1889, pp. 185-309, 
Pl. XII.-XXIV.), give diagnoses of the different tadpoles 
examined by them, but make no mention of any peculiarity in 
the position of the cloacal orifice. 
It is interesting to call to mind the well-known fact, that in 
the lung-breathing fish, Protoplerus, there is an analogous asym- 
metry in the position of the cloacal aperture, lying as it does, 
now to the right and now to the left of the median line, (cf. 
Wiedersheim, Lehrbuch d. vergl. Anat. der Wirbelthiere, 2 
Auflage, 1886, p. 563). In the specimen of Protopterus anneclens 
in the adjoining Geological Museum, it lies to the deft of the 
middle line, being placed at the side of a mesial fold of the skin, 
which is of precisely the same nature as that described above for 
the tadpole of &. clamata. 
It also recalls the condition of things in Amphiorus, where the 
anus lies constantly on the left side of the body, above the 
caudal fin. 
