ANATOMY OF UMBILICAL BAG. 143 



veins through which the portal circulation of 

 the fish is carried on ; it also contracts as it 

 becomes gradually emptied of its contents. 

 The outer sac, on the contrary, does not con- 

 tract, and has no circulation over it ; in fact, 

 its only purpose seems to be to protect the 

 very delicate inner sac. It appears to be 

 quite insensitive, as the fish is not incommoded 

 by its being cut, whereas he shows discomfort 

 if the inner sac is but touched. The sac con- 

 tains, besides the fatty matter, three or four 

 loose globules of pure oil. The liver is situ- 

 ated on the right side of the fish, just on the 

 boundary between the body and the um- 

 bilical vesicle, rather projecting into the 

 vesicle (as in the human subject the liver of 

 the infant projects beyond the false ribs), as 

 shown in drawing No. 2. On examining the 



