194 INTRODUCTION TO CONCHOLOGY. 



of being shortened or lengthened, drawn up or stretched 

 out ; and the result of this action is a progressive move- 

 ment of the slug in any direction that he wills. 



The meanest creature is an aggregate of wonders, a beau- 

 teous and elaborate piece of mechanism, which man cannot 

 imitate. 



NUCLEOBKANCHS. 



Ages have passed since storln-^vreck'd mariners 

 On old Beotia's shores found, 'mid the embers 

 Left by their beacon fire, a wondroi^ substance. 

 Which men call glass, and which in after times 

 Proved as a gift from heaven, so great its use. 

 Yet Carinaria, with her glassy shell. 

 Perchance at that same moment floated by. 



MoUusks which pertain to the above order exhibit a 

 peculiarity of organization, on account of their feathered 

 brancliise being enclosed in a nucleus projecting from the 

 back, and covered with a transparent glassy shell, in a man- 

 ner distantly analogous to the way in which the branchial 

 cavity is protected in the Ajolysm ; and although the general 



