The Digestive System 157 



pair form a fairly broad, moderately thick ring 

 muscle next to the anus that is attached anteriorly 

 to the pubis and posteriorly to the second haemal 

 process. When these muscles draw together they 

 narrow or completely close the anal slit. The 

 muscles of the other pair are broader but thinner, 

 and extend in a general dorso-ventral direction. 

 Anteriorly, above the cloaca, they are united with 

 each other, but posteriorly they separate and, 

 with the above ring muscle, are inserted on the 

 second hsmal arch. Judging from their attach- 

 ment they widen the anal opening laterally. 



The Histology of the Enteron of the 

 Florida Alligator 



It has long been known that the sea lampre}^ 

 Petromyzon marinus, during the spawning season, 

 when the body is distended with eggs, takes no 

 food, and that the digestive tract during this period 

 shrivels up until it is reduced to a mere thread. 

 This condition doubtless obtains in other forms as 

 well, though it has not been actually observed by 

 the writer elsewhere. 



A number of small alligators that were kept alive 

 in the laboratory for a year or more caused the 

 writer to wonder whether any very marked change 

 had taken place in their digestive tracts during 

 the months they took no food. 



In captivity, especially if the water in their tank 



