ALIMENTARY CANAL IN LEPIDOSIREN AND PROTOPTERUS. 515 
fused ventral rudiments, but between stages XXXIV and 
XXXV the dorsal surface of the right ventral pancreas comes 
in contact with the ventral surface of the dorsal pancreas, 
and fusion promptly takes place, so that from now onwards 
there is a single pancreatic complex. 
By stage XXXV the pancreatic complex forms a voluminous 
organ, the dorsal end of which is visible in a dissection from 
the dorsal side (cf. text-fig. 13 of Lepidosiren at this stage), 
lying immediately to the left of the dorsal lobe of the liver — • 
between it and the junction of fore- and mid-gut, and ex- 
tending back in the spiral groove. This dorsal pai-t of the 
complex extends ventrally downwards into the posterior limb 
of a saddle-shaped mass, which bestrides the bile-duct, and 
which represents the fused right and left pancreatic rudi- 
ments, the original right rudiment having now become pos- 
terior in position. The threefold origin of the pancreas is 
still betrayed by its three attachments to the gut, the original 
right and left ventral being now immediately posterior and 
anterior to the point of junction of bile duct and gut, while 
the long fine duct, which represents the long drawn-out stalk 
of the dorsal pancreas, opens in the posterior angle between 
fore-gut and mid-gut. The right and left ventral attach- 
ments are still solid. Tlie substance of the gland itself is 
seen in sections to be undergoing obvious histological diffe- 
rentiation, and to be penetrated by a rich network of blood- 
vessels. 
By stage XXXVI the pancreas Inis become actively func- 
tional, and its cells have attained their definitive character 
with nucleus at outer end, and the main mass of the cell 
protoplasm being packed with zymogen granules. With the 
tucking in of the gut wall to form the spout-like pyloric 
valve, the opening of the dorsal pancreatic duct is carried 
inwards, and is now found to open into the cavity of the 
spout-like structure, the actual opening being on the dorsal 
wall of the spout. 
Lepidosiren. — In Lepidosiren the general features of 
pancreas development are as in Protopterus, with minor 
VOL. 54, HART 4. — NEW SERIES. 37 
