746 MICROSCOPIC FORMS OF ANIMAL LIFE - PROTOZOA 



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

 actively for a time ; later on, they probably settle down to develop 

 themselves into the parental form. 



The Amoeban like the Actinophryan type shows itself in the 

 testaceous 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 resembling in constitution the chitin which 

 gives solidity to the integuments of insects ; it is usually discoidal 

 (fig. 579, 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, &c. cemented together. 

 In each of these genera the sarcode-body resembles that of Amoeba 

 in every essential particular, the contrast being very marked be- 

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

 inosculating pseudopodia of Gromia (fig. 571). In each case a de- 

 tached portion of the sarcodic body will put forth pseudopodia of 



. 579. Testaceous forms of Amoeban rhizopocls : A, Ditfittt/ia 

 proteiformis ; B, Difflugiu oblonga ; C, Arcella acuminata ; D, 

 Arcella dentata. 



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 propa- 

 gation among the amcebans thus inclosed. In Arcella it has been 

 observed that the pseudopodia of two or more individuals unite hy 

 bridges of protoplasm, and afterwards separate ; and it seems to be 

 almost certain that this is a true 'conjugation,' and not a mere 

 ' zygosis.' A remarkable method of reproduction has been observed 

 by Gruber in E-uglypha alveolata ; in an active form highly refractive 

 bodies, which, seen from the surface, look like discs, are to be found 

 beside the nucleus. Reproduction commences with the protrusion 

 of protoplasm from the orifice of the test, and, later on, the just- 

 mentioned bodies pass out also, and form a covering for the extruded 

 protoplasm ; in about an hour the process is complete, but the new 

 or daughter-cell is still without a nucleus. This is derived from that 

 of the mother, which increases in size, elongates greatly, and then 

 becomes constricted; the anterior portion passes into the daughter- 

 cell. Here we have the remarkable phenomena of the formation of 

 the test by the parent-cell and the rare case of division of the 

 protoplasmic body preceding that of its nucleus. 



