RHIZOPODA. 11 



from a primordial segment, sometimes in a straight line, more 

 commonly in a spiral curve ; and eacli segment so developed 

 has its own shelly envelope. As, however, they are organically 

 connected, the whole seems to form a " chambered " or " poly- 

 thalamous " shell. The last-formed segment is usually 

 distinguished by the very long, slender, pellucid, colourless, 

 contractile filaments which have suggested the name " Bhizo- 

 pocls " for the class. But, in the Foraminifer a, both the outer 

 wall and the septa of the compound shell are perforated by 

 minute apertures, through which either connecting or pro- 

 jecting filaments of the soft organic tissue can pass. The 

 several segments or jelly-filled chambers are essentially 

 repetitions of each other ; and there is no proof that the inner 

 and earlier segments derive their nourishment from the outer 

 and last-formed one. A foraminifer may therefore be regarded 

 either as a series of individuals, organically united, or as a 

 single aggregate being, compounded according to the law of 

 vegetative repetition. 



The minute chambered shells of Foraminifer a enter 

 largely into the composition of all the sedimentary strata, 

 and are so abundant in many common and familiar materials, 

 like the chalk, as to justify the expression of Buffon, that the 

 very dust had been alive. The deep-sea soundings of the 

 Atlantic Telegraph Company, and those since taken midway 

 between Bockall and Cape Farewell, have shewn that the bed 

 of that great ocean, at a depth approaching, or even exceeding, 

 two miles, is composed of little else than the calcareous shells 

 of a Glohigerina and a few other Bhizopods, with the silicious 

 shields of the allied Polycystinece. The composition of the 

 chalk is extremely similar : when the finer portion, amounting 

 to half or even less, has been washed away, the remaining 

 sediment consists almost entirely of foraminated shells, some 

 perfect, others in various stages of disintegration. They have 

 also been found in other marine formations, which are soft 



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