18 THE MICROSCOPE AND ITS REVELATIONS. 



further advance upon the Amoeban type. The substance of its body ex- 

 hibits a very clear differentiation between the homogeneous hyaline ecto- 

 sarc (B, a, d), and the contained endosarc, which contains such a multi- 

 tude of spherical vacuoles, #, as to have a ' vesicular ' or frothy aspect. 

 When it feeds upon the decomposing vegetable matter at the bottom of 

 the pools it inhabits, its body acquires a blackish hue; but in other sit- 

 uations it may be colorless. Besides the vacuoles, there are seen in the 

 endosarc a great number of nucleus-like bodies, e, e, and also many hya- 

 line globular brilliant bodies, /, /, which are regarded by Greef as germs 

 or swarm-spores, developed from nucleoli set free within the general cav- 

 ity of the body by the bursting of the nuclei. This creature, during the 

 active period of its life, moves like an Amoeba, either by general undula- 

 tions of its surface, or by special pseudopodial extensions d. After a 

 time, however, its movements cease, and it looks as if dead; but by the 

 giving- way of its ectosarc, a multitude of minute amcebiform bodies break 

 forth, each having its nucleus and contractile vesicle. These at first live 

 as Amoeba, but afterwards pass into a resting state, assuming a spherical 

 or oval shape, and then put-forth flagella, by which they swim actively 

 for a time, probably then settling-down to develop themselves into the 

 parental form. 



Fia. 291. 



Testaceous forms of Amoeban Rhizopods: A, Difflugia proteiformis; B, Difflugia oblonga\ c, 

 Arcella acuminata; D, Arcella dentata. 



407. The Amoeban like the Actinophryan type shows itself in the testa- 

 ceous as well as in the naked form; the commonest examples of this being 

 known under the names .Arcella and Difflugia. The body of the former 

 is inclosed in a ( test ' composed of a horny membrane, apparently resem- 

 bling in constitution the chitine which gives solidity to the integuments 

 of Insects: it is usually discoidal (Fig. 291, c, D) with one face flat and 

 the other arched, the aperture being in the centre of the flat side; and 

 its surface is often, marked with a minute and regular pattern. The test 

 of Difflugia, on the other hand, is more or less pitcher-shaped (A, B), and 

 is chiefly made up of minute particles of gravel, shell, etc., cemented to- 

 gether. In each of these genera, these sarcode-body resembles that of 

 Amc&ba in every essential particular; the contrast being very marked be- 

 tween its large, distinct lobose extensions, and the ramifying and inoscu- 

 lating pseudopodia of Gromia (Fig. 283). In each case a detached portion 

 of the sarcodic body will put forth pseudopodia of its own type; and the 

 separation of a bud or gemmule put forth from the mouth of the test seems 

 to be an ordinary mode of propagation among the Amoebans thus inclosed. 

 In Arcella it has been observed that the pseudopodia of two or more 

 individuals unite by bridges of protoplasm, and afterwards separate; but 

 it seems doubtful whether this is a true generative ' conjugation,' or a 

 mere 'zygosis.' It has been observed by Butschli, however, that after 

 the separation of three individuals which had been thus united, the sar- 



