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ELEDONE. 505 
surface of the liver (fig. 17), and the two organs are sur- 
rounded by a common iridescent membranous envelope, 
outside and in addition to their individual coverings. 
In a freshly obtained Eledone a bilobed oval whitish 
region can be distinguished round the origin of the two 
hepatic ducts (Pl. VIII, fig. 32, P.). This is the so-called 
pancreas, and shows up distinctly against the yellowish 
green liver. The digestive gland as a whole is soft and 
spongy, and enclosed in a very delicate membranous 
envelope. It is built up of branching secretory tubules 
which open into the hepatic ducts. The pancreatic 
tubules likewise open into these ducts, further down. 
According to Bourquelot, the digestive hepato- 
pancreatic fluid poured into the spiral caecum is 
colourless before digestion, and brownish after it. The 
hepatic secretion consists of diastase, trypsin and pepsin, 
while the pancreas secretes diastase also. 
The opaque rather thick-walled hepatic ducts run 
posteriorly, and after embracing the intestine unite to a 
common channel which enters into the spiral caecum 
(fig. 28). Hence the order of events in the digestive 
economy of Hledone is as follows :— 
(1) Food seized by the suckers is torn up by the jaws 
and passed into the mouth. 
(2) Here it is mixed with the mucous secretion of the 
sub-lingual and posterior salivary glands. 
(3) Next the radula rasps it and further breaks it up. 
(4) As it passes into the oesophagus the secretion of 
the anterior salivary glands is poured over it. 
(5) Now it passes to the stomach. Here the food is 
ground and mixed well. The hepato-pancreatic ferments 
enter from the caecum or reservoir, and become mixed 
with the food, and so digestion takes place. 
(6) Next the food passes on out of the stomach into 
