MANY-CHAMBEKED SHELLS. 17 



time pushed out, much after the manner in which they werp 

 at first drawn in. 



The class of animals to which, the Amoeba and the Actino- 

 phrys belong, comprise two great divisions, in one of which the ani- 

 mals are simple, and in the other associated together in compo- 

 site structures, forming, as it were, a common body, though it 

 is not improbable that each segment of the composite animal 

 still retains, to a certain extent, an independent existence. 

 Most of the solitary kinds are lodged in a horny capsule or shell, 

 which, in the different species, assumes a flask-like, bell-shaped, 

 or globular form, through a narrow opening in which the enclosed 

 animal projects its gelatinous pseudopeas, whether in search of 

 food or for the purpose of locomotion. The composite species 

 are all enclosed in calcareous shells, which, though in most of 

 the forms exceedingly minute, are yet of a very complicated 

 structure, and exceedingly beautiful objects for the microscope. 

 These shells are divided into a number of distinct chambers, and 

 are perforated with numerous foramen, or holes, from which 

 characters they derive their two technical names of Polytha- 

 lamia, or many-chambered, and Foraminifera, or perforated, 

 shells. The circumstance that these tiny structures consist of 

 several chambers arranged in various spiral forms, like the 

 shells of the Nautilus and its extinct allies, led to the belief at 

 one time that the animals inhabiting them were microscopic 

 members of the Nautilus family. But more accurate examina- 

 tion has shown that, unlike what is seen in the Nautilus, every 

 chamber of these microscopic shells is inhabited ; and that the 

 occupant of each chamber is, in some sort, an independent being, 

 which throws out its delicate filaments through the perforations 

 of its chamber-walls, just as the Amoeba does from the naked 

 surface of its body. 



All the Foraminifera are inhabitants of the sea, and in some 

 1 tarts they abound in such vast profusion as to be gradually 

 producing extensive deposits of calcareous matter by the accu- 

 mulation of their almost invisible shells. The remarkable eleva- 

 tion which stretches across the bed of the Atlantic, between 

 Cape Clear in Ireland and Cape Race in Newfoundland, and 

 which is now well known as the " telegraphic plateau," from the 

 circumstance that it was upon this ridge that the Atlantic telegra- 

 phic cable was laid in the summer of 1858, appears to be thickly 



c 



