Ammocoetes

“ The enormous interest of this muco-cartilage consists in the fact that it forms very well-defined plates of tissue, entirely confined to the head-region, which are not found in any higher vertebrate, not even in the adult form Petromyzon, for every scrap of the tissue as such disappears at transformation.
It is this evidence of primitive non-vertebrate tissues, which occur in the larval but not in the adult form, which makes Ammocœtes so valuable for the investigation of the origin of vertebrates. ”

“ Look how it is marked."
"That's an ammonite," I said, glad to know the first thing she asked.
"An am-mo-nite?" said she. "Yes; go on," and she nodded her head.
So I told her what little I was able, how the ammonite had once been a living sea-creature, swimming about in the ocean; and how it had somehow died out, so that no ammonite was ever found now alive; and how the only ones ever seen were these fossil ammonites, which had lived so very, very long ago, that their remains were turned to stone. ”

“ A section, a hundred feet thick, will exhibit, at different heights, a dozen species of ammonite, none of which passes beyond its particular zone of limestone, or clay, into the zone below it or into that above it; so that those who adopt the doctrine of special creation must be prepared to admit, that at intervals of time, corresponding with the thickness of these beds, the Creator thought fit to interfere with the natural course of events for the purpose of making a new ammonite. ”

“ As the cells of plants change into roots or leaves or bark, when leaves or roots or bark are needed, so all the different parts of animals, from the amoeba up to man, have been made to grow by the work they, have to do. The amoeba uses all parts of itself for the same purposes. There is no part that always does the walking—so it has no legs or feet. The legs and feet which the amoeba makes, as it wants them, are called " false feet." It has no stomach that always stays a stomach, because there is no part that it always uses to digest its food. ”

“ Destroy the organism utterly—burning the fragments — else there is no telling what might happen. The amoeba, as I have explained, reproduces by simple division. Any fragment remaining might be dangerous.”
Lee took the rubbery, translucent giant cell—but he did not obey orders. Instead of destroying it as his father had directed, Lee thought out a plan. Suppose he should grow this organism to tremendous size? Suppose, when the tale of his father's accomplishment were spread, an amoeba of many tons weight could be shown in evidence? ”

“ The dysentery amoeba is a clear, faintly greenish-tinted, transparent body, some three to five times the diameter of a red blood-corpuscle. In its vegetative phase it is recognizable by its movements, which closely resemble those of the ordinary fresh- water amœba. The faintly granular endosarc surrounded by the very clear ectosarc is distinguishable. The nucleus may sometimes be detected in the endosarc, as well as one or two non-contractile vacuoles, and, generally, various extraneous bodies such as blood corpuscles, bacteria, and so forth, which the amoeba has included. ”

“ The geographical distribution of Ammonites in the ancient world, seems to have partaken of that universality, we find so common in the animals and vegetables of a former condition of our globe, and which differs so remarkably from the varied distribution that prevails among existing forms of organic life. We find, the same genera, and, in a few cases, the same species of Ammonites, in strata, apparently of the same age, not only throughout Europe, but also in distant regions of Asia, and of North and South America. ”

“ By removing them in succession in the adult form we find an illustration of the evolution of the elaborate shell of the Jurassic Ammonite. It is an admirable testimony to the validity of the embryonic law we have often quoted—that the young animal is apt to reproduce the past stages of its ancestry—that the order of the building of the shell in the late Ammonite corresponds to the order we trace in its development in the geological chronicle. About a thousand species of Ammonites were developed in the Mesozoic, and none survived the Mesozoic. ”

“ The Sorophora of Zopf (Acrasiae of Van Tieghem) are a group of microscopic organisms inhabiting the dung of herbivorous animals and other decaying vegetable matter. As Pinoy (26) has shown, the presence of a particular species of bacteria with the spores is necessary for their hatching and as the essential food of the amoebulae which emerge from them. There is no flagellate stage, and it is in the form of amoebulae, multiplying by fission, that the vegetative stage of the life history is passed. At the end of this stage numbers of amoebulae draw together to form a “pseudo-plasmodium.” ”

“ Ammonoidea.—Shell multiform, straight, curved, flat spiral, or turreted, sutural line more or less complex, siphuncle simple.
Some authorities hold that the members of this great sub-order, now totally extinct, belong to the Dibranchiata, on the ground that the protoconch resembles that of Spirula rather than that of the Nautiloidea. Others again regard the Ammonoidea as a third, and distinct Order of Cephalopoda. Their distribution extends from the Silurian to (possibly) the early Tertiary. No trace has ever been found of an ink-sac, mandible, or hooks on the arms ”

“ The internal structure of these Ammonites is generally well preserved, the chambers being lined with spar or other mineral matter; transverse polished sections are often very beautiful from the several cells being occupied by variously coloured marble, susceptible of a high polish. (Pl. III.) In some examples the entire shell is transmuted into brilliant pyrites (sulphuret of iron) , and the chambers are filled with white spar; a specimen of this kind in my possession, collected by Lady Murchison, is the most elegant fossil imaginable.
Plate III.
Polished section of an Ammonite. ”

“ If finely ground colouring matter, such as carmine or indigo, is put into the water, you can see the body of the amoeba pressing these coloured particles into itself, the substance of the cell closing round them. The amoeba can take in food in this way at any point on its surface, without having any special organs for intussusception and digestion, or a real mouth or gut. ”

“ It moves, feels, nourishes itself, and reproduces. Some kinds of these amoebae can be seen with the naked eye, but most of them are microscopically small. It is for the following reasons that we regard the amoebae as the unicellular organisms which have special phylogenetic (or evolutionary) relations to the ovum. In many of the lower animals the ovum retains its original naked form until fertilisation, develops no membranes, and is then often indistinguishable from the ordinary amoeba. Like the amoebae, these naked ova may thrust out processes, and move about as travelling cells. ”

“ As was suggested in the introduction, there is no good reason for supposing that the causes of streaming in the various organisms in which it is observed are fundamentally different. The problem of ameboid movement cannot be considered apart from the streaming of protoplasm in foraminifera, myxomycetes, plant cells, lymphocytes, desmids, diatoms and ciliates. The streaming of endoplasm in some cells, such as in ciliates and plant cells, does not give rise to change of shape of the cell as it does in ameba. ”

“ These complicated edges of the septa form the delicate and intricate lines of foliation (sutures) seen on the casts of Ammonites (Lign. 156, fig. 2) , Baculites (Lign. 161, fig. 3) , Hamites, &c. In some species the shell is thick and dense, as in the Ammonites of the Kimmeridge Clay near Aylesbury, in which one species (Ammonites biplex, Min. Conch. pl. ccxciii.) in particular abounds, and is very generally invested with the shell, as perfect as if recent. The same Ammonite occurs in the Portland limestone above, in the state of casts, without any vestige of the shell. ”

“ It is curious to note, therefore, that the amoeba is, in a sense, immortal-- that the living nucleus of one of these minute creatures that we examine to-day under a microscope may have conceivably drawn, out an unbroken thread of life since the remotest epochs of the world's history. Although no sexual intercourse can be observed, there is reason to believe that a process of supposed "cannabalism," in which a larger amoeba may occasionally engulph a smaller one, is really a conjugative reproductive process, and followed by increased vitality and division. ”

“ Later the amoeba verrucosa was broken up into fine spherical granular balls, and these gradually became obscured and apparently diffused among the granular contents of the endosarc of the amoeba limax. The observations from the time of the seizure of the amoeba verrucosa to its digestion or disappearance among the granular matter of the entosarc of its captor, occupied seven hours. From naked amoeba the shell-protected rhizopods were no doubt evolved, and it is a curious sight to observe them swallowed, home and all, to be digested out of their house. ”

“ I have many specimens from the lias of Whitby, of the Ammonites Communis, in which the outer chamber thus filled with spar, occupies nearly the entire last whorl of the shell, its largest extremity only being filled with lias. From specimens of this kind we also learn, that the animal inhabiting the shell of an Ammonite, had no ink-bag; if such an organ existed, traces of its colour must have been found within the cavity which contained the body of the animal at the moment of its death. The protection of a shell seems to have rendered the presence of an ink-bag superfluous. ”

“ Labyrinthula, discovered by L. Cienkowsky, forms a network of relatively stiff threads on which are scattered large spindle-shaped enlargements, each representing an amoeba, with a single nucleus. The threads are pseudopods, very slowly emitted and withdrawn. The amoebae multiply by fission in the active state. The nearest approach to a “reproductive” state is the approximation of the amoebae, and their separate encystment in an irregular heap, recalling the Acrasieae. From each cyst ultimately emerges a single amoeba, or more rarely four (figs. 6, 7) . ”

“ All these activities are egoistic. The amoeba is putting forth effort to gain its sustenance; it is sacrificing energy to receive compensation in the form of support. If we continue to watch this minute organism we will find that sooner or later it goes into a resting stage which does not last long before we can observe important internal changes making themselves manifest first at the nucleus, which slowly divides into two equal portions that separate, each carrying with it about half of the protoplasm of the parent organism. ”

“ In each of these genera it is the exterior form of the shell that is principally varied, whilst the interior is similarly constructed in all of them, to act as a float, subservient to the movements of Cephalopodous Mollusks. We have seen that the Ammonites, beginning with the Transition strata, appear in all formations, until the termination of the Chalk, whilst the Hamites and Scaphites are very rare, and the Turrilites and Baculites do not appear at all, until the commencement of the Cretaceous formations. ”

“ We have noticed that in the Devonian the sutures of some of the chambered shells become angled, evolving the Goniatite type. The sutures now become lobed and corrugated in Ceratites. The process was carried still farther, and the sutures were elaborately frilled in the great order of the Ammonites. It was in the Jurassic that the Ammonites reached their height. No fossils are more abundant or characteristic of their age. Great banks of their shells formed beds of limestone in warm seas the world over.
The ammonite stem branched into a most luxuriant variety of forms. ”

“ More than in many other mollusks the organization of the ammonite is reflected in the characters of the shell and the infancy, maturity and decline of the group to which it belongs is, to the qualified student, pictured in the characteristics of the successive portions of the lustrous coil of the fossil shell. ”

“ Many amoebæ show also in the interior a small clear space, the contractile vesicle which alternately contracts and expands, through which action the movement of the intracellular fluid is facilitated and waste products removed. The interior granules often change their position, showing that there is motion within the mass. The amoeba slowly moves along the surface of the glass by the extension of blunt processes formed from the clear outer portion which adhere to the surface and into which the interior granular mass flows. ”

“ In the vegetative stage the human amoebae are best differentiated by the nuclear structure as shown in stained specimens. In E. coli the nucleus is vesicular with a thick nuclear membrane and the chromatin chiefly deposited on the under surface of the nuclear membrane. This chromatin often seems deposited in quadrant aggregations. The karyosome is eccentric.
For the pathogenic amoeba we recognize a histolytica type of nucleus, which is found in dysenteric stools, and a tetragena type, which is found in diarrhoeal or more or less normal stools. Dobell does not recognize this differentiation. ”

“ Wherever access to it can be had, we find it richly fossiliferous; but its organisms, with the exception of its Belemnites, are very imperfectly preserved. I dug up from under the trap-blocks some of the common Liasic Ammonites of the north-eastern coast of Scotland, a few of the septa of a large Nautilus, broken pieces of wood, and half-effaced casts of what seems a branched coral; but only minute portions of the shells have been converted into stone; here and there a few chambers in the whorls of an Ammonite or Nautilus, though the outline of the entire organism lies impressed in the shale ”