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HARDWICKE'S SCIENCE-GOSSIP. 



NOTES ON AMCEBA AND INFUSORIA. 



By Bernard Thomas. 



I.— The Amceba. 



THE Amoeba is often chosen as a type of the 

 animal cell. It is a single cell without 

 modifications. For this reason and also because its 

 study is, perhaps, the best introduction to the 

 Infusoria, it is here introduced. 



The Protozoa forms the lowest group of the animal 

 series, and correspondingly the Protophyta that of the 

 plant series. These two groups, although differing 

 in some ways, resemble each other in several other 

 particulars, so that it may be doubtful in which 

 kingdom to refer a particular organism. Thus we 

 may draw a letter U, one limb of which represents 

 the vegetable and the other the animal kingdom, 

 while the connecting piece, in like manner, represents 

 the unicellular organisms common to both. Professor 

 Hackel's Protista* was intended to include that class 

 of organisms intermediate between the two large 

 biological kingdoms, but it unfortunately included 

 multicellular as well as unicellular forms. 



The Amoeba (Fig. 25), the Protean animalcule, is 

 to be found in almost all collections of ditch or pond- 

 water, and when a familiar object the microscopist has 

 usually not long to search for it. To those who 

 have never seen it, it may be mentioned that it can 

 usually be found in the water where dead flowers have 

 been left to stand. With a fair instrument, and a 

 magnifying power of two or three hundred diameters, 

 its form and movements may be readily examined. 



In size it varies, some specimens may be so large as 

 to be visible to the unaided eye, but this is by no 

 means common, and others, again, require a power of 

 three hundred diameters before they can be observed 

 with any satisfaction. Its very irregular outline is 

 constantly changing (Fig. 25 l>). The general sub- 

 stance (described as protoplasm) is transparent, 

 colourless and in places more or less granular. 

 Sometimes it contains spaces filled with a more fluid 

 material or with food, consisting of organisms, etc., 

 it has "swallowed." Usually one of these spaces is 

 contractile and known as the contractile vesicle, and 

 somewhere in the protoplasmic mass a roundish body, 

 the nucleus or endoplast, is to be distinguished. 



The protoplasm may be divided into two areas ; 

 an internal, more granular endosarc, and an external, 

 more hyaline ectosarc. The appearance may be 

 compared to that of ground glass, fine in the former 

 and coarse in the latter region. Some Amoeba are 

 niore hyaline throughout, others more granular. 



The semi-fluid nature of the protoplasm is best 

 understood by observing the formation of the pseudo- 

 podia or processes which the Amoeba ever and anon 



* Hackel's Protista : i. Monera ; ii. Flagellata ; iii. Labrin- 

 thula ; iv. Diatomese ; v. Phycochromaceas ; vi. Fungi ; vii. 

 Myxomycetes; viii. Protoplasta ; ix. Noctiluca; x. Rhizo- 

 poda. 



thrusts forth. This phenomenon takes place in the 

 following order : — 



(1.) A bulging of the ectosarc. 



(2.) The granules of the endosarc run rapidly into 

 the process so formed. 



Sometimes, however, only the first part of this 

 process is performed. The more fluid part of the 

 protoplasm is the internal endosarc, and its fluidity is 

 demonstrated by the quicker performance of the 

 second stage than of the first. 



Apart from the formation of pseudopodia, however, 

 there are movements constantly visible in the en- 

 dosarc, which may be described as a kind of 



Fig. 25. — a, Amceba, showing contractile space [c. s.), nucleus 

 («.), food-vacuoles \f. v.), and pseudopodia. The endosarc is 

 clearly marked from the ectosarc ; in the latter granules are 

 seen, b, Amoeba, showing change of form after a few seconds. 

 c, nucleus and contractile space very highly magnified. 



rotation similar to, but not so regular as, that seen in 

 certain vegetable cells. 



With respect to the granules, these seem to be of 

 two kinds, either coarse with well-defined outline, or 

 small and faint. The pres*nce of the latter is 

 explained by the theory that the protoplasm is a 

 delicate network with a fluid substance filling its 

 insterstices. The strands of the network are neither 

 rigid nor constant, and it must not be supposed that 

 they are arranged with any regularity. In places 

 their absence is denoted by a vacuole, and the 

 junction of the meshes by a granule (node). The 

 contractile vesicle, if observed for any length of time, 

 is seen to expand and contract. It has been supposed 

 by some to represent a heart driving the fluid in all 

 directions through the organism. It may be, perhaps, 

 a rudimentary respiratory organ, by which the aeration 

 of the protoplasm is brought about. But at present 

 its function is uncertain, and it may simply be a mani- 



