486 SYSTEMATIC HISTORY OF THE INEUSORIA. 



cessary here to state more than that the beings so grouped together are hete- 

 rogeneous both in nature and character, and partake scarcely any other features 

 in common than those of minuteness and the possession of one or of few elon- 

 gated cilia or filaments as locomotive organs. The deficiency of characteristics 

 necessary to constitute a natural family, and the absence of any proof of the 

 animality of the several genera, were perceived by Siebold, who rejected the 

 Monadina from his group of Infusoria. Agassiz says of them that they are 

 mostly moveable germs of various kinds of Algae ; and in this statement, we 

 beheve, as far as relates to the majority, he is correct. Dr. Biu-nett (Boston 

 Journ. Mat. Hist. 18o3,Yi.^. 319) has the following remarks on these topics : — 



"As the family Monadina now stands, it undoubtedly includes very hetero- 

 geneous elements, particles being grouped together from their general asj)ects 

 rather than from their physiological characteristics. I cannot pretend to take 

 them up in that systematic way in which they have been arranged by Ehi^en- 

 berg ; for I have found but little system about them, and for the most part 

 have been unable to follow his descriptions. If we are to judge of them by 

 mere form and size alone, I should say that the varieties they present under 

 the microscope are numberless. Indeed, in watching the same particle for a 

 long time, I have seen it change its form and size four or five times, and each 

 as distinct from the other as many of Ehrenberg's species. Those which con- 

 tain chlorophyll must, it appears to me, in virtue of that fact, be regarded 

 as of a vegetable nature. As to the others this point would be doubtful." 



Again, Dujardin, whilst admitting generally the animal nature of the ge- 

 nera in question, difi'ered widely from the Berhn natm^alist both as to their 

 organization and distribution. Since, however, in the present state of our 

 knowledge, it is impossible to fix on the organisms of which they are but de- 

 velopmental phases, it is well, for the purpose of future identification and 

 future researches, to attempt definitions and descriptions of these simple 

 beings, although, as an artificial and temporary proceeding, the whole be 

 doomed to ultimate neglect and destruction. Consequently, we shall retain 

 all Ehrenberg's genera and species, which, however iU-defined and unsatis- 

 factory, give the best representation we possess of these varied and variable 

 microscopic organisms. 



The views of Ehrenberg on the special organization of the Monadina have 

 been widely criticised and condemned. The possession of an integimient, the 

 fixed invariable outline, and the ocular nature of the red speck, are statements 

 which have encountered the opposition of Dujardin and of very many subse- 

 quent naturalists. The existence of a mouth and the recej)tion of coloured 

 food have likewise been widely denied, in accordance with the prevalent 

 hypothesis of their vegetable nature as early phases of Algae and Eungi ; but 

 latterly Cohn has witnessed the entry of coloiu^ed particles into theii' interior, — 

 a circumstance confirmed by Lachmann, who moreover adds that he has twice 

 observed Monadina which contained a smaU. Diatom, the excretion of which, 

 in the vicinity of the posterior extremity, taking place soon afterwards, also 

 made him consider the existence of an anus probable. Schneider remarked 

 in Ghilomonas Paramecium one or two reddish lines running from the inden- 

 tation into which the filaments were fixed, to the opposite end, and, from a 

 comparison of these with the process of fission as seen in Bodo, concluded 

 that they were fiurows which gradually deepen until the animalcule is bisected. 

 As during this process the being undergoes no change of form, except in be- 

 coming a little broader, and the division takes place along its whole length, 

 the process must readily escape observation. The anterior end is always a 

 little thicker ; the furrows consequently are deeper and more distinctly recog- 

 nizable in that part. It is only in rare cases, when the division has taken place 



