George Herbert Fowler

“ It seems to be the case that to every organism is assigned a minimum temperature below which it dies, a maximum temperature above which it dies, and an optimum temperature at which it thrives best; but these have to be studied separately for every species. Similarly, in regard to depth, species have been classed as eurybathic and stenobathic, but, since increased depth practically means diminished temperature, these are probably merely expressions of the same fact in another form. ”

“ The prevalent winds, dependent on the fairly constant distribution of atmospheric pressure over the great oceans, are the most important determinant of currents. As at most points in the ocean the temperature, salinity and chemical composition of the water are mainly determined by the currents—that is, by the condition at the place whence the water came—it is obvious that a study of currents must precede any general view of the distribution of marine forms. ”

“ The epibenthos is obviously that fauna to which, except in polar regions, light and warmth are necessary; and the absence of these at greater depths is probably the chief barrier to its vertical extension; the food supply is sufficiently plentiful in, at any rate, the upper parts of the mesobenthic zone to present no obvious barrier. The chemical constitution of the water (except to animals in brackish water near river mouths) and the pressure appear to exert little or no influence; and only those species which attach themselves to clean hard substances would be repelled by the mud-line. ”

“ In the first hundred fathoms at sea the fall of temperature is gradual and slight, and forms practically no hindrance to the diurnal oscillation of the oceanic epiplankton—the alleged rise and fall of almost the entire fauna. Roughly speaking, the greatest number of animals is nearest the surface at midnight; but different species sink and rise at different times, and to or from different depths. ”

“ We can only guess at the causes of the apparently limited range of many deep-sea types. (a) One of these is probably the limited food supply: presumably, as with a land fauna, there are as many mouths in a given area as it will support, and an equilibrium of species is maintained which will at least hinder the extension of any one. ”

“ The ectoderm rarely consists of more than one layer of cells: these are divisible by structure and function into nervous, muscular and secretory cells, supported by interstitial cells. The endoderm is generally also an epithelium one cell in thickness, the cells being digestive, secretory and sometimes muscular. Reproductive sexual cells may be found in either of these two layers, according to the class and sub-class in question. ”

“ For general use by less skilful students in a laboratory, price, simplicity and rapidity of work recommend the rocking microtome of the Cambridge Scientific Instrument Company, but it tends to fail at large or hard objects. ”

“ The wealth Epiplankton. of minute organisms near the surface is inconceivable to those who have not seen the working of a two-net: it may be gauged by the fact that a single species is sometimes present in such quantities as to colour the sea over an appreciable area, and by the estimate that the skeletons of epiplankton from a square mile of tropical ocean a hundred fathoms deep would yield 16 tons of lime. In the tropics the wealth of species, and towards the poles the number of individuals of comparatively few species, are characteristic of the latitudes. ”

“ Generally speaking, as might be expected, the freely-moving hypobenthos, fish and crustacean, have the widest ranges, and even these are not helped by currents, as are epibenthic or planktonic forms. The larval history of deep-water forms is, however, unfortunately obscure. (c) Lastly, extension of area of a species being at best difficult in deep water for non-swimmers, the place and date of their first migration must be taken into account; forms which have comparatively recently adopted deep-water life cannot be expected to have spread far from their original centre. ”

“ In this zone, which extends from about 500 fathoms to the greatest depths (which may in some cases exceed 5000 fathoms, or more than 51⁄2 m.) , the temperature at any given point is uniform throughout the year, and is always very low: the mean at 2200 fathoms is 35.2° F.; at greater depths and in special circumstances less than 30° F. has been recorded. The darkness is probably absolute; for food the animals are dependent upon each other and upon the incessant rain of dead plankton from higher levels; the pressure may be anything between half a ton and five tons per square inch. ”

“ In the Coelentera the ectoderm and endoderm are set apart from one another at a very early period in the life-history; generally either by delamination or invagination, processes described in the article Embryology. Between these two cell-layers a mesogloea (G. C. Bourne, 1887) is always intercalated as a secretion by one or both of them; this is a gelatinoid, primitively structureless lamella, which in the first instance serves merely as a basal support for the cells. ”

“ For the all-round work of an investigator, its simplicity and finish have made Jung’s sliding microtome with the Naples improvements deservedly popular for many years; it can be fitted with special apparatus for cutting celloidin and frozen objects, and it can be relied upon to cut any tissue, however difficult; but it cannot be worked as rapidly as some others, nor produce long ribbons of large objects. ”

“ The Indo-Pacific fauna ranges from East Africa to about 108° W., stepping from island to island over the Pacific; but this continuity is then broken by 37 degrees of longitude and more than 2000 fathoms of water, and such sessile species as are most Mollusca (cf. fig. 3) are unable to reach the American coast. This is presumably due to the fact that the planktonic larvae of epibenthic adults must settle on a suitable bottom within a certain period or die. In spite of the direct set of the currents from Florida to the British Isles, the epibenthos of the two is absolutely dissimilar ”

“ As regards the plankton of the two polar regions and such epibenthic forms as extend also into deep water, the suggestion has been made that the Arctic and Antarctic benthos and plankton are really continuous by way of deep water in the main oceans, where the organisms can find a suitably low temperature. ”

“ As regards the penetration of light, assimilative rays useful to plant life probably do not reach beyond 150 fathoms. Photographic rays have been detected as low as 220 fathoms, and if any light penetrate beyond this depth, it will consist only of blue, violet and ultra-violet rays: it has been suggested that the red colour prevalent in many deep-sea animals may be a screen from these hurtful rays. ”

“ Hence few if any littoral species are circumpolar. For example, not a single littoral Ophiurid surrounds the South Pole, but five or six species are circumpolar in the northern hemisphere.
Taking next the mesobenthos and hypobenthos, living at depths where temperature is constant and current practically negligible, Mesobenthos; Hypobenthos. there appears theoretically to be no reason why an organism which can thrive at 500 fathoms should not have a world-wide range over the bottom of all oceans. ”

“ This process can be greatly hastened by the use of a partial vacuum. When impregnation is complete the paraffin is cooled rapidly, so as to assume a homogeneous non-crystalline condition, and the tissue thus comes to form part of a block of soft but tenacious material, which protects it from damage by air or damp, and can be readily cut by a razor. The block is then trimmed to the form of a triangle or rectangle, and fixed by a clamp or by local melting in the holder of the microtome. ”

“ While the bottom water of the ocean is very cold, and the midwater of a more or less intermediate temperature, the surface water, according as it has drifted from the equator polewards or in the reverse direction, has a mean annual temperature somewhere between 84° and 30° F., losing or gaining heat on its way. ”

“ The sections, when cut by the microtome with the knife straight and the two sides of the rectangular paraffin block parallel to it, in most cases can be got off in a continuous ribbon, each sticking to its predecessor. This very desirable result generally can be insured by a coating of softer paraffin; but if the object be large, or brittle, or of varying texture, it is safer to cut the sections singly from a triangular block with an oblique knife. The sections or ribbon are often not quite flat, but rolled, creased or compressed; they must be flattened before being attached to the slide. ”

“ But it is not to be supposed that all our present-day deep-water forms began their migration simultaneously, and we can say with fair certainty that migration to deep water did not begin before the close of the Mesozoic epoch. ”

“ The knife is flat on one side and hollow-ground on the other. In using the microtome it is essential that the cutting edge of the knife points towards the end of the instrument where the handle is placed; the hollow-ground face should be uppermost, and the flat surface should not be exactly horizontal but slightly inclined so that the lower facet of the cutting edge is parallel to the frame. As to the relation of the position of the knife to the direction of motion, it is the usual practice, when paraffin sections are to be taken, to have the cutting edge at right angles to the motion ”

“ It is then transferred to one of a group of reagents, which are miscible with absolute alcohol, but would form an emulsion with water, and are solvents of the embedding medium. The embedding mass in most general use is paraffin wax, melting at a temperature of 54° to 60° C., according to the character of the object and the thickness of section required. The object is transferred from absolute alcohol to benzol, chloroform, cedar oil, or similar fluid to the melted paraffin; the fluid diffuses and evaporates, leaving the tissues to be completely permeated by the paraffin. ”

“ The first automatic microtome suitable for cutting a block of tissue into a continuous series of sections was made in 1883 in the university Workshops of Cambridge, from a design by W. H. Caldwell and R. Threlfall. Only a single machine was made, but in 1884 twelve machines were made by the Cambridge Scientific Instrument Company from a design by Caldwell. ”

“ This single cavity and its lining serve apparently for all those functions (digestion, excretion, circulation and often reproduction) which in more complex organisms are distributed among various cavities of independent and often very diverse origin. ”

“ It is necessary at the outset to divest oneself of these errors; oceanic conditions depend only very indirectly upon the distribution of the land, and strongly swimming or freely floating animals are not to be confined by the same factors as determine the distribution of sessile forms, whose range is governed by a variety of circumstances. ”

“ It is very doubtful whether this enormous pressure makes the slightest difference to marine invertebrates, the tissues of which are uniformly permeated by fluids, so that the pressure is uniform in every direction; but animals with free gases naturally require time to adjust the gas-pressure when altering their levels. ”

“ Apart from this diurnal oscillation, unfavourable conditions at the surface send or keep the fauna down in a remarkable way: for example, in the Bay of Biscay few organisms are to be found in the first fathom in bright sunlight, but on a still, hot day the next few fathoms teem with life ”

“ The general processes of the dry method employed in zoological and botanical microtomy are, up to a certain point, practically identified with those used for the preservation of animals and their tissues for other branches of microscopic work. In the first place the tissues must be killed ”