446 REPRODUCTION OF RHIZOPODA. 



organisms like the Foraminifera, or by any Siliceous-shelled 

 organisms like the Polycystina.* 



334. Reproduction of RMzopoda. — Very little is certainly 

 known respecting the processes by which the multiplication of 

 Rhizopods is effected. It may often be seen that portions of the 

 sarcode-body detached from the rest can maintain an independent 

 existence ; and it is probable that such separation of fragments 

 is the ordinary mode of increase in this group. Thus when the 

 pseudopodian lobe of an Amoeba has been put-forth to a consider- 

 able length, and has become enlarged and fixed at its extremity, 

 the subsequent contraction of the connecting portion, instead of 

 either drawing the body towards the fixed point, or retracting the 

 pseudopodian lobe into the body, causes the connecting band to 

 thin-away until it separates; and the detached portion speedily 

 shoots out pseudopodian processes of its own, and comports itself 

 in all respects as an independent Amoeba. It is an interesting 

 exemplification of the intimacy of the relation between the form 

 of the pseudopodia and the properties of the sarcode-body of the 

 Rhizopoda, that any small separated portion of that body will 

 behave itself after the characteristic fashion of its type ; thus, if 

 the shell of an Arcella be crushed, so as to force out a portion of 

 its sarcode, and this be detached from the rest, it wili soon begin 

 to put forth lobose extensions like those of an Amoeba ; whilst if 

 the like operation be performed upon a Polystomella, or any other 

 of the Foraminifera, the detached fragments of the protoplasm will 

 extend itself into delicate ramifying and inosculating pseudopodia 

 resembling those of Gromia. We shall find that the production 

 of the 'polythalamous' (many-chambered) shells of Foraminifera is 

 due to a repeated gemmation or budding of the sarcode-body ; 

 and there can be no reasonable doubt that in such ' monotha- 

 lamous ' (single-chambered) forms as Gromia, Arcella, and 

 Difflugia, similar buds are put forth, but become detached before 

 they develope their testaceous envelopes. There is evidence, again, 

 that in such naked forms as Act 'in ophrys and Amoeba, multipli- 

 cation takes place by a binary subdivision resembling that of 

 Protophytes. Thus it may often be observed that the spherical 

 body of Actinophrys is marked by an annular constriction, which 

 gradually deepens so as to separate its two halves by a sort of hour- 

 glass contraction ; and the connecting band becomes more and 

 more slender, until the two halves are completely separated. This 

 process of fission, which may be completed within half an hour 

 from its commencement, seems to take place first in the Contractile 



* For more detailed information respecting Amoeba and its allies, the 

 reader may be specially referred to the Memoir of Dr. Auerbach in 

 " Siebold and Kolliker's Zeitschrift," Band vii., 18.56 ; to the " Etudes sur 

 les Infusoires " of MM. Claparede and Lachmann ; and to the elaborate 

 series of Papers by Dr. Wallich in the "Annals of Natural History, 

 3rd Ser., Vols. xi.. xii., xiii., 1863 and 1864. 



