132 GENERAL HISTORY OF THE INFUSORIA. 



This power of the Monadina to become polymorphic is likewise alluded to by 

 Mr. Carter (A. N. H. 1856, vol. xviii. p. 122). 



According to modem phraseology, we might describe these beings as com- 

 posed of protoplasm enveloped by a pellicle, and as having an extension of the 

 protoplasmic mass developed in the form of a flagelliform filament, to serve 

 as a locomotive organ. The presumed gastric cells are the vacuoles in the 

 protoplasm hollowed out spontaneously within it, and ever changing in posi- 

 tion and magnitude. Dujardin affirms that they at times form near the 

 surface, open externally, and on again closing up include foreign particles 

 which have found their way within them, and that they thus act in some 

 measure as instniments of nutrition in aid of the general process carried on 

 by endosmose or absorption. 



That the Monadina had a mouth communicating with the ' gastric sacs,' 

 Ehrenberg believed to be demonstrated by the introduction of particles of 

 colour within those cavities from without. " The nutritive apparatus," he 

 tells us, '^ may be readily seen in some species in their ordinary state (for 

 instance, in Monas guttula and M. vivipara), whilst in others it is proved by 

 using coloured food (for example, in Monas Termo and 31. socialis). It consists 

 of several distinct or separate cells (from 8 to 20), not all filled at the same 

 time, but one after the other. These are always invisible when empty, but 

 when filled with limpid fluid appear hke so many lucid vesicles." Cohn states 

 that he can confirm the accuracy of Ehrenberg's observation of the entrance 

 of colouring particles into some Monads, and therefore inclines to the belief 

 that such examples must have an oral apertiu'e, and be of an animal nature 

 {Entiv. p. 162). To this he adds that many of the Monads of Ehrenberg 

 may really be swaiin-spores of microscopic Eungi ; still he holds it to be 

 improbable that true plant-cells should take up within them indigo-particles. 

 So, at p. 148, when remarking on the precise similarity in all visible features 

 of the swarm-spores of Achlya jprolifera with Trichodina grandinella and 

 Bodo saltans, he says Ehrenberg's Bodo eats indigo -particles, which is not 

 the case with the form in question. 



What weight should be attached to these observations of the reception of 

 molecules of colour within Monadina, as pro\dng a mouth and stomach-cells, 

 must be decided by further experiments. Sometimes, possibly enough, when 

 the minuteness of the objects concerned is remembered, the colour-grains 

 have not actually been within, but above or below them, on the surface ; and, 

 again, other experimenters damage the force of the argument by affirming that 

 they have succeeded in getting colour taken up by Diatomeae, and by undoubted 

 vegetable-cells. This statement has been made, among others, hy Braun. 



After the consideration given in a previous page to the nature of the 

 supposed eye -specks, further reference to them here is uncalled for. 



Concerning the modes of multiplication, the great Berhn micrographer is 

 correct in his account of the process of fission ; yet few will join with him in 

 describing ova and vi^dparous reproduction among Monadina, or in imagining 

 distinct male and female generative organs — in other words, an hermaphrodite 

 (monoecious) structure. Certainly the phenomenon Weisse witnessed in 

 Chlorogonmm euchlorum, of the development and subsequent discharge of a 

 host of young germs, might be termed viviparous reproduction ; but it is no 

 other than the usual plan of development of microgonidia among Algae. In 

 fact, no one has witnessed the development and extrusion of germinal ova, 

 although the breaking up of the substance of Monadina into minute particles, 

 by the process of diffluence or by often-repeated fission, and the reproduction 

 of gonidia may be constantly noticed. Perty so far countenances Ehrenberg's 

 views as to affirm the development of Monas vivipara and of M. Lens by 



