From protozoa or protista to plants and animals the graduation is closer than from magnetised iron to vitalised sarcode.
In the rhizopods--the remarkable protozoa whose unicellular organism sheds so much light on the obscure wonders of life--we notice a curious streaming of the granules in the living plasm.
But there are also complete intermediate forms between the two groups--for instance, the chrysomonades and the gymnodinia; these may behave alternately as protozoa or protophyta.
Many of the aquatic protophyta and protozoa have the power of autonomous and independent locomotion, and this often has the appearance of being voluntary.
This is seen in a glance at the one hundred and forty plates on which I have depicted thousands of these graceful little protozoa in my monograph (Challenger Report, vol.
As we count these unnucleated protozoa among the oldest and simplest organisms, and trace them directly by metasitism to the plasmodomous chromacea, it is very probable that they turned to parasitism very early in the history of life.
The unicellular protophyta exhibit the same form of metabolism and plasmodomism as the familiar green cells of the tissue-plants; but in most of the protozoa we find special features of nutrition and plasmophagy.
Among the simplest fresh-water protozoa are the arcellina or thecolobosa (difflugia, arcella), little rhizopods that are distinguished from the naked amoebae by the possession of a firm envelope.
In a large section of the higher protozoa differentiated organs of movement are developed, which may be compared to the muscles of the metazoa.
In the nucleated cells of most of the protophyta and protozoa it is more complicated, as the nucleus becomes active as the central organ and regulator of the metabolism.
This was long before the role of any insect as a carrier of pathogenic micro-organisms had been established, and before the Protozoa were generally regarded as of importance in the causation of disease.
Nearly all the Protozoa are microscopic, except when, as in the case of the Sponges, they form an aggregation of individuals.
The Amorphozoa or shapeless animals include many of the Protozoa and sponges; they have no typical form, and most of them are sessile.
The whole of the animal kingdom is divided into two great groups, which are called the Protozoa and the Metazoa.
Here, therefore, I will mention only one of them--and this because it furnishes what appears to be another important distinction between the Protozoa and the Metazoa.
These cases serve to bridge this distinction between Protozoa and Metazoa, of which therefore we may now take leave.
And if it be objected that encystation and spore-formation in the Protozoa are not always preceded by conjugation, the answer would be that neither is oviparous propagation in the Metazoa invariably preceded by fertilization.
The first is, that in some of the Protozoa processes very much resembling those of karyokinesis have already been observed taking place in the nucleus preparatory to its division.
But, if any one were so foolish as to do so, it would be easy to dislodge him by describing the state of matters in some of the Protozoa where a number of unicellular "individuals" are organically united so as to form a "colony.
Certain of the protozoa harbor within them cells of algæ utilizing to their own advantage the green chlorophil of the algæ in obtaining energy from sunlight and in turn giving sustenance to the algæ.
Variation does not seem to be so marked in the protozoa as in the bacteria, though this is possibly due to our greater ignorance of them as a class.
The trypanosomes are widely distributed, exclusively parasitic, flagellated protozoa which live in the blood of a large number of animals and birds (Fig.
It is common to all of the protozoa to develop forms which have great powers of resistance, this being due in some cases to encystment, in which condition a resistant membrane is formed on the outside, in others to the production of spores.
There are few bacterial diseases which are localized in the blood, but many of the diseases caused by protozoa have this localization.
Most of the diseases in animals caused by bacteria and protozoa are not transmitted to man, but there is a conspicuous exception.
If we regard the living things on earth from the narrow point of view as to whether they are necessary or useless or hostile to man, the protozoa must be regarded as about the least useful members of the biological society.
The protozoa are the most widely distributed and the most universal of the parasites.
The food of protozoaconsists chiefly of other organisms, particularly bacteria, and they are classed with the animals.
The universal distribution of the protozoa is due to this; the spores or cysts can be carried long distances by the wind and develop into active forms when they reach an environment which is favorable.
While the latter insists on calling themProtozoa (Primitive Animals) the former would have them Protophyta (Primitive Plants).
They differ so completely from all other forms that it has been proposed to make for them a special group, the Mesozoa, or Midway animals, between the Protozoa and all the rest of the animal kingdom.
The masterly work of Tyndall and Louis Pasteur in doing for the bacteria and protozoa what Redi had done for the larger organisms, is too much a matter of modern contemporary history to need recital here.
Footnote 4: Calkins, Studies on the Life History of Protozoa (Archiv f.
The protozoa of cockroaches and termites are clues to the relationship between these two groups of insects.
Sex produced in theprotozoa of Cryptocercus by molting.
Protozoa as indicators of developmental stages in molting of the roach Cryptocercus.
The protozoa of Cryptocercus can be transferred from one individual to another (Nutting and Cleveland, 1954).
Honigberg, 1953): Protozoawhich are normally only found in C.
In no case were the protozoarecovered from the stomach alive.
The effects of molting on the protozoa of Cryptocercus.
The ciliates Nyctotherus and Balantidium, flagellates Lophomonas and Polymastix, the amoeba Endamoeba blattae, and three unidentified protozoa were killed by this treatment, yet the insects lived normally after defaunation.
The wood-feeding roach Cryptocercus, its protozoa, and the symbiosis between protozoa and roach.
With notes on other intestinal protozoaof the cockroach.
If this is correct, and if in the protozoa the chromatin has the same influence that it seems to have in higher animals, the mode of reproduction in Difflugia would be expected to give little more than random sampling of the germ plasm.
Recent students of the StromatoporA| seem disposed to promote them from the province of Protozoa to that of the Hydroids.
Supposing these to be all, it is remarkable that we have no Protozoa or Corals or Echinoderms, and that the types of Brachiopods and Crustaceans are of comparatively modern affinities.
Sponges may be regarded as the highest or most complex of the Protozoa or the lowest of the Coelenterates.
Or again,—“The formation of new species, which among the lower Protozoa could be achieved without amphigony, could only be attained by means of this process in the Metazoa and Metaphyta.
The Protozoaand Protophyta are now included by him in the same category as the Metazoa and Metaphyta, as regards all matters of individual variation, reproduction, subjection to the law of natural selection, and so forth.
The majority of the Protozoa cannot long continue to reproduce themselves a-sexually without becoming degenerate, or rather without becoming altogether extinct.
This term is applied to a process observed in the Protozoa (q.
But Darwin ably argues in favour of each of them by pointing to well-known analogies, drawn from the vital processes of living cells both in the protozoa and metazoa.
Since the above was written Professor Weismann has transferred this doctrine from the Protozoa to their ancestors.
It is sufficient to say that the parasitic protozoa are for the most part entozoal in habit, not a few of them possessing vegetable affinities.
Passing to those protozoa which, although retaining some vegetable affinities, are more or less distinctively animal, I notice the obscure organisms termed psorosperms.
As regards the higher forms of protozoa it must suffice to allude to the Cercomonas hominis of Davaine, found in the dejections of cholera patients, to the Cerc.
All unicellular beings, such as the protozoa and the simpler algæ, fungi, etc.
The Protozoa all agree in having the body composed for its whole lifetime of a single cell,[7] but they differ much in shape and appearance.
Among all these ocean Protozoa none are more interesting than those belonging to the two orders Foraminifera (fig.
All of the animals of the ocean depend upon the marineProtozoa and the marine Protophyta, one-celled plants, for food.
Examine a drop of such water with the compound microscope, and find in it a few small, active, transparent creatures, larger than the Paramoecium and other Protozoa in the water and which have the appearance shown in fig.
It is thus evident that the Protozoa is an ancient group of animals.
For a long time, however, they were classed by naturalists with the Protozoa on account of their size.
And it is necessary that these Protozoaexist in such great numbers, for they and the marine one-celled plants (Protophyta) supply directly or indirectly the food for all the other animals of the ocean.
The marine Protozoa are the only animals which live independently; they alone can live or could have lived in earlier ages without depending on other animals.
Many of the familiar Protozoa of the fresh-water ponds always have two whiplash-like flagella projecting from one end of the body.
Age of E Laurentian Plants Protozoa O T Z i not O m I e determinable C Harper & Brothers New York.
In a great many protozoathere exists a curious pulsating cell-like body, called the contractile vesicle, which seems to be a rudimentary organ, whose function is unknown.
The lowest Protozoa are entirely without any system of colouring; being merely of uniform tint, generally of brown colour.
Thus in the:-- Structureless protozoa there is no varying colouration.
Of the lowest forms, the hydras, nothing need be said here, as they are so much like the protozoa in their simplicity of structure.
That the Protozoa are practically colourless and structureless.
The protozoa are generally very minute, and always composed of structureless protoplasm.
These protozoa possess, as it were, only negative properties.
We can, then, appeal most confidently to the protozoa as illustrating the morphological character of colouration.
The invertebrata are divided into sub-kingdoms, of which the protozoa form one.
The discovery of Gruber and others, that Protozoa are only capable of restitution if they contain at least a fragment of the nucleus, has also been used occasionally as a proof of the morphogenetic importance of the nucleus.
It has been known for many years that the Protozoa are also capable of a restoration of their form and organisation after disturbances, if at least they contain a certain amount of their nuclear substance.
