40 LESSON V. 



with inequalities on the surfaces, as spines 01 

 tubercles, which do not appear in the young 

 shell. I will now give you a summary of the 

 lesson of to-day. 



The mollusca are often placed in situations of 

 great danger. They are exposed to the dashing 

 of the waves, often borne by the violence of 

 storms and cast against rocks or stones. Others 

 placed in rapid rivers are occasionally hurried 

 along by the impetuosity of the stream. God, 

 however, always makes a suitable provision for 

 the circumstances under which he places his 

 creatures, and if he apportions to them spots of 

 danger, arms them with the means of protection 

 and defence. Thus we find that the shell and 

 the habits of the mollusca are adapted to the si- 

 tuations which they occupy. Some that belong 

 to the rapid rivers of America have an exceed- 

 ingly hard and substantial shell, fitted to contend 

 with the most boisterous elements ; others, on 

 the contrary, by their very lightness are enabled 

 to float on the surface of the water, and, offering 

 no resistance, are gently carried along by its 

 waves. Some anchor themselves securely by a 

 byssus to rocks, and thus bid defiance to danger. 

 Others by adding to the weight of their bark can 

 descend and seek a shelter in the bed of the 

 ocean. There are many other beautiful con- 

 trivances for their preservation. But in spite of 

 these a breach is sometimes made in their shell, 

 and then they have the power of repairing it by 

 exuding a calcareous matter, similar to that with 

 which they at first constructed it. 



