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blood are mixed together as represented by the brown colour.

It is interesting to observe that in nature there are no great steps from the higher animals to those which occupy a lower position in the scale of being. The descent is not abrupt but gradual, and may be represented by an inclined plane. Birds and Mammals are found to approximate each other by the Apterix on the one hand, and the Ornithorhyncus on the other.

The transition from the three-lobed heart of reptiles to the four-lobed heart of mammals is not abrupt as is evident by an examination of the annexed diagram, fig. 19, which represents the heart and circulation of the crocodile. An analogous arrangement has been just discovered in the circulating apparatus of the tadpole.

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In Fishes the circulation is still more sluggish than in reptiles. The heart simply propels the

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blood through the gills. It has to pass through the system without any additional force further than that resulting from the contractions of the arteries. Figure 20 represents the circulation of fishes.

The heart of Crustaceans and Mollusks, as represented in fig. 21, is placed in the oxygenated blood.

The dorsal vessel acts the part of a heart in Insects, and a speck has been discovered in the lowest forms of animals, such as the Amaba, Actinophrys Sol, &c., as seen is figures 22 and 23,

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which represent two of the unlimited number of

FIG. 22.

FIG. 23.

forms assumed by the Proteus or Amæba.

Every where thus we find in the great volume of Nature unity combined with diversity, preparing our minds to expect the observance of the same great law in all that the Creator has effected.

NOTE H.-THE INFLUENCE OF LIGHT.

"The relation of all organized beings to light, &c."—Page 14. The influence of light on chemical action is well known to every practical chemist. Light turns black the various salts of silver, &c., and thus it paints an image of every object upon a sensitized film, as is every where seen in the productions of photographers. Chlorine also and hydrogen gases remain in the dark, mechanical mixtures, but are chemically combined with explosion, under the influence of light, forming Hydrochloric Acid. Chlorine water-i.e., water impregnated with chlo

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rine-is kept in the dark, since in the sunlight the chlorine unites with the hydrogen of the water and oxygen is liberated.

The extent of the influence of light is pretty well understood now, in the wide domain of inorganic chemistry; but the measure of that influence in the various processes of life remains to this time, for the most part, a mystery. In reference to the result of a series of scientific experiments on the subject, the following statements may be made :

1.-That if potatoes in the process of growth be partially exposed to the sunlight a deadly poison— solanine-is developed, which may be separated by maceration in dilute sulphuric acid. Pigs have been poisoned by eating these potatoes. Light is essential to the formation of this poison. Similar remarks might be made in reference to a large number of vegetable secretions.

2. That if the ova of frogs be exposed to a continuous stream of light, natural or artificial, often intensified by passing through a combination of lenses, the tadpoles are hatched and metamorphosed sooner than otherwise, and the most diminutive or liliputian frogs are produced.

3. That fungi have been developed in perfect darkness, and tadpoles have gone though their natural metamorphosis in the absence of light. But

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in all the cases tried, (by me* as yet,) the bread, leather, &c., on which the fungi have grown, and the ova of the frogs, had been previously exposed to the light. Light, at this stage, may have exerted sufficient influence on the ova to secure the growth of the fungi, and the change of the tadpoles, as the fecundation of the ovum of an Aphis suffices for the fertilization of several generations.

The late soundings in the Atlantic ocean have thrown some interesting light on this subject. It is well known that light diminishes rapidly in passing through any dense medium, such as water; so that at a depth of 400 or 500 fathoms there is absolute darkness. It was formerly believed, therefore, that nothing living could exist at a lower depth than 600 fathoms. The recent survey of the North Atlantic, however, proves the existence of living beings far below the assigned limit. Millions of Foraminifera of the species Globigerina are found to exist at a depth of nearly two miles, and several star fishes (Ophiocoma) have been brought to the surface alive from the depth of 1260 fathoms containing the shells and remains of Globigerinæ in their stomachs, proving the existence of both at this immense depth.

* The plan adopted by all experimentalists has been similar.

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