430 VERTEBRATE LIFE AND ORGANIZATION 



.,■2 TO 20 MONTHS . 



Figure 22.5. The life cycle of the sea lamprey in the Great Lakes. The lamprey 

 spends all but a year or two of its six and one-half to seven and one-half years of life 

 as a larva. (From Applegate and Moffett: Scientific American, April 1955.) 



flow freely. From the mouth cavity, the food enters a specialized 

 esophagus that by-passes the pharynx to lead into a straight intestine. 

 There is no stomach or spleen. A liver is present, but the adult has no 

 bile duct. The intestine does not receive bile from the liver, but the 

 liver functions as a site for the storage and conversion of much of the 

 absorbed food brought to it by the circulatory system. A separate pan- 

 creas is not present, but pancreatic tissue is embedded in the wall of 

 the intestine and liver. 



Since a lamprey is often attached to another fish by its buccal 

 funnel, water cannot pass into the mouth and out of the gill slits in 

 respiration, as it does in most fishes. Instead, a pumping action of the 

 pharyngeal region moves water both in and out of the seven gill 

 pouches through as many external gill slits. Each pouch is lined with 

 highly vascular gills and connected with the pharynx through an 

 internal gill slit. The mixing of food and water is prevented, however, 

 by the separation of the pharynx from the digestive passages. The 



