438 Dr. G. C. Wallich on Amoeba villosa 



that of the true nucleus, and which is derived in all probability 

 from the sarcoblasts already referred to, becomes first aggregated 

 in that region. It only remains to be further noticed regarding 

 the nucleus, that in that condition of the organism in which a 

 very limited quantity of foreign matter is present, and the crys- 

 talloids, nucleated corpuscles, and sarcoblasts are most abun- 

 dant, this organ frequently undergoes subdivision — two separate 

 nuclei occurring under these circumstances, and sometimes, but 

 much more rarely, three. Endogenous subdivision (that is, 

 endogenous with reference to the capsule) does not take place in 

 such cases, but nucleus and capsule both undergo complete and 

 simultaneous binary division. I am unable to say whether, in 

 those examples that present three nuclei, the whole of these be- 

 come separated by one duplicative act or by two. It has already 

 been shown that where the multiple nuclear bodies supervene 

 on the accumulation of granular matter at the posterior portion 

 of the Amoeba, I failed to trace any capsular coverings. It 

 seems probable, therefore, that, in the former case, the process 

 may be regarded as one of simple fission, in the latter, of mole- 

 cular segregation*. But on this head anything like positive in- 

 formation is still wanting. 



Great diversity of opinion seems to exist amongst naturalists 

 not only regarding the office, but also the actual structure of the 

 "contractile vesicle." That misapprehension should exist on 

 the subject is by no means surprising, however, when we bear 

 in mind that the name has been indiscriminately applied both 

 to the rhythmically contracting organ of the Rhizopods and of 

 the true Infusoria, and that, under the supposition that identity 

 of action involves identity of conformation, a true vesicular wall 

 has been assigned by several of our most eminent writers to the 

 pulsating cavity of the former group of organisms. Without 

 entering at present upon the question whether the Hhizopods 

 ought to be regarded as unicellular, multicellular, or altogether 

 devoid of cell-structure, I would observe that, if the presence of 

 such structure within the substance of certain members of the 

 Amoeban group has not been already demonstrated by the per- 

 haps less definite examples adduced by Carter and others, the 

 indisputable envelopment cf the nuclear body of Amoeba villosa 

 by a distinct membranous capsule at once settles the point. 

 But, on the other hand, my own observations tend to prove that 

 this structure is only to be met with in the two higher orders of 

 the llhizopods, and not in the lowest order, which, according to 



* Carter describes a somewhat similar process as occurring in Amoeba 

 radiosa, and " ending in the production of a mass of spherical, delicate, 

 transparent, granuliferous cells." (See his paper on the Organization of In- 

 fusoria, Ann. Nat. Hist, ser. 2. vol. xviii. p. 225.) 



