ALIMENTARY CANAL IN LEPIDOSIREN AND PROTOPTERDS. 513 
p ter US the lung apparatus is in process of attaining to a 
mediodorsal position, the hinder half of the large right lung 
having already done so. In Ceratodus the whole of the 
lung except glottis and air duct has attained to the mid- 
dorsal position, and the original left lobe has apparently been 
completely withdrawn into the lung, so that the latter is a 
single structure without any paired appearance. It is clearly 
but a step from the Ceratodus condition for the air duct to 
become shortened and the glottis to reach the neighbourhood 
of the mesial plane dorsally, such dorsalward migration of the 
glottis being aided by the tendency of the gut to become 
rotated in a counter-clockwise direction, as seen from the 
tailward end.^ 
V. Pancreas. 
There are in the Dipneumona, as in Ceratodus and the 
majority of Vertebrates, three pancreatic rudiments, one 
dorsal and two ventral. 
Protopterus. — The dorsal rudiment is the first to make 
its appearance (about stage XXXII) in the form of a solid 
projection from the dorsal surface of the yolk practically in 
the mesial plane. In some embryos of this stage the dorsal 
pancreatic rudiment is greatly elongated in an aiitero-posterior 
dii’ection — possibly a reminiscence of some unknown earlier 
phylogenetic condition (text-fig. 12, a). In most embryos, 
however, the dorsal pancreas is of compact and rounded form 
(cf. text-figs. 8 , B, and 12, b), and is situated in about the 
same transverse plane as the hinder nephrostome of the 
pronephros. The attachment of the dorsal pancreas becomes 
rapidly constricted to form a narrow stalk, and a small, 
irregular cavity appears in the interior of the organ. 
By stage XXXIII the ventral rudiments have made their 
appearance in the form of a yolky projection from the gut on 
' Moser (‘Arch, iiiikr. Anat.,’ Ixiii, 1904, p. 562) has demonstrated the 
existence of this in ontogeny. See also the interesting paper by H. Marcus 
(‘ Arch, inikr. Anat.,’ Ixxi, 1908), who is led by his studies on the kmg of 
Gymnophiona to a similar conclusion regarding the hmg of Ceratodus. 
