CONUS CONE. 59 



water to the edge of the lips has any of the 

 liquid run over ? 



Child. No ; the shell holds the water like 

 a cup. 



Teacher. When this is the case, the mouth 

 is said to be contracted. But observe what is 

 the consequence when I attempt to fill a cone 

 with water up to the lips. 



Child. The water runs out before it reaches 

 the lips. 



Teacher. Examine where the liquid flows 

 out, and what is the cause of this difference in 

 the two shells. 



Child. The water flows out at the base of 

 the cone. In the other shell the lips are united ; 

 in the cone they are separated by a small 

 channel. 



Teacher. This channel is called a sinus, from 

 the Latin sin us, a curved line. If the two 

 lips be separated by a sinus, liquid poured 

 in overflows before it reaches the lips ; the aper- 

 ture iii this case is called effuse, from the 

 Latin fus us, which signifies poured out. You 

 have no doubt heard the term effusion applied 

 to the overflowing of any liquid ; you ought now 

 to know exactly what such an expression means. 

 Compare the columellar lip with the correspond- 

 ing part of the Cone in these shells (a Voluta 

 and a Cypraea.) 



Child. It is smooth. 



Teacher. Examine all your Cones, and see 

 whether they are all quite smooth. 



