62 LESSON IX. 



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 yp 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 aperture 

 in this case is called effuse, from the Latin fu- 

 sus, which signifies poured out. You have no 

 doubt heard the term effusion applied to the 

 overflowing of any liquid ; you now know exactly 

 what such an expression means. Compare the 

 columella with the corresponding part 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. 



Child. No ; there are stripes at the base of 

 some of them. 



Teacher. These are called strict, the Latin 

 for stripes. Are they only perceptible to your 

 sight! 



Child. I can feel them also. 



