130 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
tadpole* and Marsipobranch, and the entire absence not 
only of horny teeth and sucking mouth, but of larval meta- 
morphosis, such as is exemplified by our common Frogs, 
in both the Urodela, and Xenopus (Dactylethra) the most 
completely aquatic Batrachian in existence.t On the 
Parkerian hypothesis this ought not to be so. These 
facts and numerous others akin to them, which have 
arisen during the recent study of metamorphosis and 
‘‘nursing’”’ among the amphibia and other Ichthyopsida, t 
point much more natually to the conclusion that the well 
known characters and provisional appendages of the larval 
Anura are, together with the various types of external 
gills formed among the Urodela, secondarily acquired and 
adaptive; and that the only structures conspicuous during 
metamorphosis at all recapitulatory in the sense implied, 
are the internal gills, with their associated skeletal and 
vascular arches,§ and the tail. 
In the various publications dealing with the sucking 
mouth of the vertebrata, the extent to which that struc- 
ture is represented among the living Chimeeroids has been 
insufficiently recognised. The labial cartilages of Callor- 
hynchus (fig. 5, Pl. X), as originally pointed out by 
Johannes Muller in his monumental ‘‘ Myxinoiden”’ (op. 
cit.) attain a development unparalleled among the higher 
onathostomata. While agreeing in their fundamental rela- 
*See Schulze, Abhandl. Akad., Berlin, 1888. Héron Royer and Van 
Bambeke, Archy. d. Biol. Tm. IX, p. 185, and Gutzeit, Zeitschr. f. Wiss. 
Zool. Bd. XLIX, p. 43, cf. also Beard op. cit. 
+ cf. Leslie and Boulenger, Proc. Zool. Soc., Lond., 1890. p. 69. 
tef. Boulenger, Ann. and Mag. Nat Hist., Ser. v., Vol. XVII, p. 463 ; 
Ser. vi., Vol. I, p. 454, and Vol. II, p. 122; also Fletcher Proc. Linn. Soe. 
N.S.W., Ser.ii, Vol. IV, p. 357 ; and Wood Mason and Alcock Proc. R. Soc., 
Lond., Vol. XLIX, p. 359, and Vol. L, p. 202. 
§ Approached from this standpoint the position of the Der ‘tremata in the 
Amphibian series receives a fresh significance. 
