122 LABORATORY WORK. 



the animal into exactly symmetrical halves. The septa 

 through which this plane passes are the directives. Do 

 they correspond in position to the siphonoglyphes? Study 

 a few of the incomplete septa. Have these muscles like 

 the others? At the oral ends of the septa look for open- 

 ings (septal ostia) through these partitions. 



Split the other part of the animal lengthwise and pin 

 out under water. Notice that the oesophagus does not 

 reach the base. Could food pass from the oesophagus into 

 the inter- and intraradial chambers? Do you find any 

 body-cavity distinct from the digestive cavity? Do you 

 find any opening to compare with a vent? 



Along the free edges of the mesenteries are the coiled 

 mesenterial filaments. Do they present the same appear- 

 ance nearer the oral disc that they do farther down? On 

 the sides of the septa near the mesenterial filaments are 

 the reproductive organs (not always plainly visible). 



