Hydroid

“ Amongst plants it has long been known that the direction of light or of gravity may determine where roots or branches or other morphogenetic formations are to arise; in hydroids also we know that these factors of the medium may be at work41 as morphogenetic causes, though most of the typical architecture of hydroid colonies certainly is due to internal causes, as is also much of the organisation in plants. ”

“ Occasionally one is fortunate enough to discover these small jellies in a pool where they can be photographed as they pulsate back and forth. When these attain their full size they lay eggs which sink to the bottom and grow up into the plant-like hydroids. So each generation of these interesting creatures is entirely unlike that which immediately precedes or follows it. In other words, a hydroid is exactly like its grandmother and granddaughter, but as different from its parents and children in appearance as a plant is from an animal. ”

“ The polyps also include the salt water animals called hydroids, jellyfishes, and coral polyps.
Hydroids.—Figure 40 shows a hydroid, or group of hydra-like growths, one of which 29eats and digests for the group, another defends by nettling cells, another produces eggs. Each hydra-like part of a hydroid is called a hydranth. Sometimes the buds on the hydra remain attached so long that a bud forms upon the first bud. Thus three generations are represented in one organism. Such growths show us that it is not always easy to tell what constitutes an individual animal. ”

“ Like many other compound Hydroids, the sexes are never combined, in one of these communities; they are always either male or female, and as those with female buds have not yet been observed, we can only judge by inference of their probable character. Front what is already known, however, of Hydroid communities of a like description, we suppose that the process of reproduction must be the same in these, and that the female stocks of Nanomia give birth to small Jelly-fishes, the eggs of which become oil bubbles, similar to that with which our little community began. ”

“ In this way the little animals live, day after day and year after year, patiently waving their tentacles, and waiting for the food that is sure to come.
Do you still ask what connection there is between these demure little animals and the jolly jelly-fish? We shall soon see.
The hydroids have grown by budding and branching somewhat as plants do. Occasionally pear-shaped cups much larger than those we have looked at are formed on the stem. These large cups are called spore-sacs. They contain the substances which, later, will grow into eggs; and at the proper time they fall off. ”

“ In the case of the hydroids, the power of budding, a power which is almost absent in insects, enables the larval life to assume a degree of importance which it could not have if the larva remained simple, for it has rendered division of labor possible, and has produced polymorphic communities, most of the members of which are out of the line of succession. ”

“ Hydrox′yl, a compound radical not yet isolated, but found in many chemical compounds.
Hydrozoa, hī-dro-zō′a, n.pl. (sing. Hydrozō′on) one of the main divisions of the sub-kingdom Cœlenterata, the other two being Ctenophora and Anthozoa or Actinozoa; they are chiefly marine organisms, soft and gelatinous, free or fixed, existing everywhere, endlessly varied in form and complexity of structure, including such great groups as hydroids, acalephs, medusans, jelly-fish, sea-blubbers, &c.—adjs. ”

“ Only they are in nature not vegetable, but animal. Many of these ocean blooms are exquisitely beautiful; but they may not always be gathered with impunity.
“Ocean-lamps,” too, many may with truth be named. Large numbers of the coral-polyps, large numbers of the hydroids, and perhaps [p. 198] all of the free-swimming medusæ or jelly-fishes, carry with them their own little lanterns, wherewith at night to make bright the surface of the sea—wherewith also to bear glimmers of light downward into those black depths where sunlight cannot reach. ”

“ They absorb the marine salts, they assimilate the solid elements in the water, and since they create coral and madrepores, they’re the true builders of limestone continents! And so, after they’ve finished depriving our water drop of its mineral nutrients, the droplet gets lighter, rises to the surface, there absorbs more salts left behind through evaporation, gets heavier, sinks again, and brings those tiny animals new elements to absorb. The outcome: a double current, rising and falling, constant movement, constant life! ”

“ The first specimen I ever possessed of the beautiful confervoid Hydrodictyon utriculatum was obtained in this way—the water, after depositing a green sediment, gave birth to a rich net-work of vegetation, in which this conferva was conspicuous. Several of the jars which I prize the most are those which have been simply filled at the brook side, and left for the minute germs of animal and vegetable life to develope in their own way, and it is not long before a rich growth takes place, that affords abundant material for observation with the microscope. ”

“ The quantities used are so large as to render it difficult to maintain an adequate supply, and the errors resulting from the use of any water fit for drinking purposes are too slight to be perceptible, so long as no considerable development of the animal and vegetable germs is allowed. Water containing the slimy filaments of fungoid growths and moss protonema, algae, vorticellae, etc., will not only cause errors by obstructing the stop-cock at low velocities, but these organisms will cause a coalescence of sediments that defies any ordinary churning, and completely vitiates the operation. ”

“ These beads and bubbles are pure oxygen, which the plants distil from the water itself, in order to obtain its hydrogen, and from carbonic acid, in order to obtain its carbon.
There is one more feature, which no writer on the aquarium has yet noticed, namely—when a tank is properly stocked, the water soon gets crowded with infusorial animalculæ, which swarm among the plants, and on the sides of the glass in countless thousands, visible only by the aid of the microscope. These are in accordance with a natural law; the presence of vegetable matter in water always induces them. ”

“ The Common Gases dissolved or imprisoned by well and spring water are carbonic acid, sulpurretted hydrogen and the components of air—oxygen and nitrogen. Of these only one is dangerous—sulpurretted hydrogen—and that is easily detected by its smell, resembling that of spoiled eggs. It gives the characteristic odor to “sulphur” waters. Carbonic acid and air give to waters their sparkling quality—the former being often artificially introduced, as in “soda-water,” &c.
The Organic Matter in well, spring, and river water may be dead or living, and we will consider the two classes separately. ”

“ The constituent parts of pure water, in volumes, are two parts of hydrogen and one of oxygen, and by weight one part hydrogen and eight parts oxygen. When pure it is transparent, tasteless, inodorous, and colorless, except when seen in considerable depths. But having such high solvent powers and affinity for almost every substance in nature, one can account for suspicions that science places on all waters, for it is never free from impurities. And well it may not, if doctors are to be believed, for they tell us, that chemically pure water is not best for man ”

“ Surface water sinks into porous soils and rocks, and accumulates in pockets and veins which feed springs, and are the reserve water supply that keeps our rivers flowing, even through dry weather. More water is held by absorption in the earth's solid crust than in all the oceans and seas and great lakes.
Hydrogen, combined with carbon, occurs in solid rocks where the remains of plants and animals have slowly decayed. From such processes the so-called hydrocarbons, rock oil and natural gas, have accumulated. When such decay goes on above ground, these valuable products escape into the air. ”

“ The solution of mineral matter by ground water, as well as the other chemical changes it effects, is greatly augmented by the impurities, especially carbonic and other organic gases, dissolved by the water from the atmosphere and the soil. The commonest chemical changes effected by the joint action of water and air, oxidation and carbonation, have been referred to in Chapter II. Hydration is more exclusively the work of water, and is one of the commonest processes of rock change, and often of rock disintegration. ”

“ Between the branches of the algae, gasteropods and other animals become completely enclosed by the growing plants, while diatoms, foraminifera, and other forms of life are abundant. Water percolating through the mass gradually destroys the structure of the algal thalli, and in places reduces the whole bank to a compact structureless limestone. ”

“ Hydration and dehydration.—Water sometimes unites directly with some of the constituents of a rock and produces hydrated minerals, i.e., minerals that have water as an element of their constitution, not simply water absorbed into their pores. A large class of minerals known as zeolites, because they swell up and undergo life-like contortions when their basic water is driven off by heat, are examples of hydrous products. ”

“ Water is an actual necessity to the plant not only as a direct food and food-solvent, but as the vehicle of important inorganic materials. The hydrogen, too, of the organic compounds is obtained from the decomposition of the water which permeates every part of the plant, and is derived by it from the soil and from the aqueous vapour in the atmosphere. The chief chemical substances of which vegetable protoplasm is constituted are six, viz, potassium, magnesium, calcium, iron, phosphorous, and sulphur. ”

“ Moreover, plants adapted to arid conditions are usually provided with additional safeguards in the form of thick, non-conducting layers of surface cells, or long channels connecting the interior tissue with the breathing-pores on the surface. Often hairy, scaly or viscous coverings serve the same end. On the other hand, when the air is very moist, so as to check evaporation, water is sometimes found secreted in minute droplets around the breathing-pores of the leaves, since its ascent is a necessary condition of nutrition and development. ”

“ If a little real sea-water, even a pint or two, can be obtained to mix with the artificial, the ripening of the latter will be considerably hastened, but it is an interesting fact in the chemistry of the aquarium that, though in the first preparation of sea-water certain of the ingredients are left out of the prescription, in process of time those very same ingredients are to be discovered in it by means of analysis. ”

“ Before any specimens are placed in the tank, they ought to be rinsed with sea-water, and any barnacles or sponges scraped off the pieces of rock to which the plants are attached. Any neglect of this will be sure to be followed by the production in the tank of sulphuretted hydrogen, which blackens and kills all before it. Nor should any animal that appears exhausted be consigned to the tank until it has been kept some little time in a shallow bowl with a few weeds, and revived by the occasional use of the syringe. ”

“ Hence it seems probable that the clay is merely the insoluble residue or ash, as it were, of the organisms—the delicate shells, as they slowly sink to the more profound depths, being dissolved by the free carbonic acid, which, as observations would seem to shew, occurs rather in excess at great depths. Thus we see how the organic forces may give rise to extensive accumulations of inorganic matter, closely resembling the finest silt or mud which is carried down to the sea by rivers, and distributed far and wide by ocean currents. ”

“ The entire water-cure system is founded upon fresh air and water. And you see, Karl, how wisely nature has provided; we go about in the open air, and we breathe in the black carbonic acid, and the nitrogen, for they cannot be separated, and then comes the water-cure and turns these ugly things out of doors, for the oxygen of the water unites with the carbonic acid, and the hydrogen drives out the nitrogen from the body, in the sweating process. ”

“ When these processes continue for a long time in deep water shut off from free circulation so that it does not become aerated by contact with the atmosphere the water becomes unfit to support the life of fishes, and when the accumulation of putrefying organic matter gives rise to sulphuretted hydrogen as in the Black Sea below 125 fathoms, life, other than bacterial, is impossible. ”

“ The ionization of water, slight as it is, yields hydrogen-ion and hydroxide-ion, the ions characteristic of acids and of bases, and water is placed among the weakest of the acids (see table, p. 104) as well as among the weakest of the bases (table, p. 106) . We shall return to these relations, presently, and shall find that the apparent weakness of water, as a base and as an acid, is seemingly very largely due to the fact that water represents only an extremely dilute solution (see p. 66) of the real hydroxide, HOH, or hydrol, and consists very largely of a compound (H2O) 2. ”

“ The power of the organic colloids to imbibe water, and to bring along with it into their substance the materials which work transformations, would not be continuously operative if the water imbibed were to remain. It is because it escapes, and is replaced by more water containing more materials, that the succession of changes is maintained. Among the higher animals and higher plants its escape is facilitated by evaporation. And the rate of evaporation is, other things equal, determined by heat. ”