OF THE PROTOZOA. EHIZOPODA. 227 



no genus he has examined, has he been able to discover its shell to be com- 

 posed of calcareous spicula, such as Carter represents in OpercuUna Arahicay 

 and refers to as indicative of the intimate affijiity between Foraminife^xi and 

 sponges, in the ensuing j^aragraph {A. N. H. x. 1852, p. 173) : — '' It must 

 be now generally allowed that the Rhizopodous nature of Foraminifera is 

 identical with that of the Amoeba or Proteus, and through the latter with the 

 Sponge-cell ; and in addition to this, we have the former, at least the genus 

 Operculina, stiU more nearly aUjing Foraminifera to the Sponges, by possess- 

 ing a spicula structui^e, if not a circulating system also, like that of 

 SjDonges." 



The calcareous sheU of Rhizopoda is lined (XXI. 16) within by a delicate 

 organic homogeneous membrane, with a sharp outline, and of a more or less 

 deep-broAvn colour. It is in immediate contact with the animal, and closely 

 apphed to the shell, and has the same perforations (XXI. 24). It penetrates 

 from one chamber to the next through the intermediate pores and canals. 

 Duiing life it is, in the last-formed chambers, colourless. It is not equally 

 visible in all species. By the addition of dilute acid to Botalia, Rosalina, and 

 Textilaria, it is readily brought into \dew ; but in Miliolida this is difficult, 

 o^ving to its dehcacy and want of colour. In the first-formed (primordial) 

 chamber, occupied by colourless substance, it would seem to be absent. In 

 its chemical relations it resembles the chitinous shell of Gromia, and is so 

 very slowly destroyed by decomposition, that it may be demonstrated in 

 empty shells found amidst the sand at the sea- side, and, according to d'Archiac 

 and Jules Haime, even in fossil specimens. 



Dimensions and Conditions of Life of Rhizopoda. — The size of the Rhi- 

 zopoda is very varied, even among members of the same genus. Ehi-enberg 

 describes Amoehoi fi'om ^ l^^ th and i^J-jjth to y^th of an inch ; Difflugice from 

 g-JfTo-tli? and YY,Vuth to T^th, and ArceUce from yy-o-th to ^xo^^ ^^ ^^ inch. 

 Between individuals even of the same species, he represents a diversity of 

 size of nearly equal extent. Schultze states the diameter of the shells of 

 Gromia oviformis, and of G. Diijardinii, to be -gyth of an inch, whilst that of 

 Lagynis is only tt-J ,jth in length. Dujardin remarks that the largest fresh- 

 water Rhizopoda attain a diameter of -^2^(^, whilst the marine Foraminifera 

 are for the most part visible to the naked eye, and have a length of from ^^^th 

 to -i-th of an inch. The Xautiloid shells of PolystomeUa have a diameter of 

 gL-th to 2yth of an inch, and the ii'regularly- chambered AcervuUnce a length 

 of fi'om Jjtt^ to -1th of an inch. Among fossil Foraminifera larger sizes 

 prevail : thus. Sir E. Belcher brought one species from Borneo measuring more 

 than 2 inches in diameter ; and many Nummulites are found an inch and 

 upwards in diameter. 



Mr. Jeffreys gives the following account of the habits of Foraminifera 

 (Proc. Roijal Soc. 1855) : — "■ Most are free, or only adhere by theii' pseudo- 

 podes to foreign substances. Such are the Lagena of Walker, Nodosaria, Vor- 

 ticiaJis, and Textidaria, and the Miliola of Lamarc. The last genus has some, 

 although a very limited, power of locomotion, which is effected by exserting its 

 pseudopodes to their fiiU length, attaching itself by them to a piece of seaweed, 

 and then contracting them like india-rubber, so as to draw the shell along with 

 them. Some of the acephalous mollusks do the same by means of theii' bj^ssus. 

 This mode of progression is, however, exceedingly slow ; and I have never 

 seen, in the course of 24 hoiu-s, a longer joui^ney than a quarter of an inch 

 accomplished by a Miliola. . . . Some are fixed or sessile, but not cemented at 

 their base like the testaceous Annelids. The only mode of attachment appears 

 to be a thin film of sarcode. The Lohatida of Fleming, and the Rosalia and 

 Planorhidina (D'Orb.) belong to this division. Dr. Cai^Denter considers the 



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