for the explanation of which we look in vain to any at present known cause.

I must plead the fact of the existence of such wonderful phenomena as those alluded to, as my apology for thus attempting to come forth with what, although they may appear crude, theoretical notions, yet may, as tending to direct increased attention to important phenomena, so lead in due time to the development of truth, and extend the present bounds of our knowledge to those mighty laws which are so mysteriously indicated by the existence of the phenomena in question, and with the evidences of which we are yet surrounded.

A course of observations on the solar spots and on the remarkable features which from time to time appear on the sun's surface, which I have examined with considerable assiduity for several years, had in the first place led me to entertain the following conclusion, namely, that whatever be the nature of solar light, its main source appears to result from an action induced on the exterior surface of the solar sphere, a conclusion in which I doubt not all who have attentively pursued observations on the structure of the sun's surface, will agree.

Impressed with the correctness of this conclusion, I was led to consider whether we might not reasonably consider the true source of the latent element of light to reside, not in the solar orb, but in space itself; and that the grand function and duty of the sun was to act as an agent for the bringing forth into vivid existence its due portion of the illuminating or luciferous element, which element I suppose to be diffused throughout the boundless regions of space, and which, in that case, must be perfectly exhaustless.

Assuming, therefore, that the sun's light is the result of some peculiar action by which it brings forth into visible existence the element of light, which I conceive to be latent in, and diffused throughout, space, we have but to imagine the existence of a very probable condition, namely, the unequal diffusion of this light-yielding element, to catch a glimpse of a reason why our sun may, in common with his solar brotherhood, in some portions of his vast stellar orbit, have passed, and may yet have to pass, through regions of

space in which the light-yielding element may either abound or be deficient, and so cause him to beam forth with increased splendour, or fade in brilliancy, just in proportion to the richness or poverty of this supposed light-yielding element as may occur in those regions of space through which our sun, in common with every stellar orb, has passed, is now passing, or is destined to pass, in following up their mighty orbits.

Once admit that this light-yielding element resides in space, and that it is not equally diffused, we may then catch a glimpse of the cause of the variable and transitory brightness of stars, and more especially of those which have been known to beam forth with such extraordinary splendour, and have again so mysteriously faded away; many instances of which abound in historical record.

Finally, in reference to such a state of change having come over our sun, as indicated by the existence of a glacial period as is now placed beyond doubt by geological research, it appears to me no very wild stretch of analogy to suppose, that in such former periods of the earth's history, our sun may have passed through portions of his stellar orbit in which the light-yielding element was deficient, and in which case his brilliancy would have suffered the while, and an arctic climate in consequence spread from the poles towards the equator, and leave the record of such a condition in glacial handwriting on the everlasting walls of our mountain ravines, of which there is such abundant and unquestionable evidence. As before said, it is the existence of such facts as we have in stars of transitory brightness, and the abovenamed evidence of an arctic climate existing in what are now genial climates, that renders some adequate cause to be looked for. I have accordingly hazarded the preceding remarks as suggestive of a cause, in the hope that the subject may receive that attention which its deep interest entitles it to obtain.

This view of the source of light, as respects the existence of the luciferous element throughout space, accords with the Mosaic account of creation, in so far as that light is described as having been created in the first instance before the sun was called forth.

Report on the Investigation of British Marine Zoology by means of the Dredge. Part I. The Infra-littoral Distribution of Marine Invertebrata on the Southern, Western, and Northern Coasts of Great Britain. By Professor EDWARD FORBES.

(Continued from page 391 of Vol. LI. of Philosophical Journal.)

Gregarious and prolific species.-Many of our littoral mollusca, as the shore-living species of Littorina, Purpura, Trochus, Cardium, Donax, Mya, Pholas, &c., are truly gregarious, and the individuals of each are constantly found assembled together in considerable numbers. This is not so commonly the habit among sub-littoral species; among them, however, there are some habitually gregarious (as Ostrea edulis, &c., and among radiata, Ophiura rosula, Uraster rubens, Comatula europæa, Echenus sphæra), though with this difference as compared with the most littoral gregarious forms, that whereas the individuals of the latter are always assembled together, the sub-littoral species are gregarious in some zones of depth and under certain conditions of sea-bottom, while they are at the same time diffused in small numbers, or even as solitary individuals in situations where the conditions do not seem so favourable to fecundity. Many species also, not at all gregarious in the true sense of the word, having a very wide range in depth, are not equally prolific throughout that range, but are developed in much greater numbers in one region than in another, or in different parts of the same region, according to the conditions of the sea-bed. Climatal differences also have a considerable effect in determining the prolific or non-prolific character of a species, and this may be observed clearly, even in such a limited area as that under review. Hence, when we state of many species that they are diffused throughout all the provinces of that area, it is not to be understood that they are equally abundant, so far as their individuals are concerned, in all. Thus, for example, Dentalium entalis is distributed throughout the British seas; but whilst it is so abundant as to be almost gregarious in the northern provinces, it becomes scarce and solitary in the southern. Many examples of this may be seen by consulting the analysis of dredging papers in the preceding tables, and afterwards comparing them with the tables of enumeration of localities of species.

In the Littoral region, as mentioned already, the species of Littorina, Trochus, Patella, and Purpura are most abundant, and among bivalves, Mytilus edulis, Cardium edule, and Kellia rubra. These with many other animals, and with peculiar marine plants, give a character to the sea-belt between the tide-mark.

In the Laminarian region, extending from low water-mark to 15 fathoms or thereabouts, Lacuna and Rissoæ are abundant.

Between 15 and 25 fathoms in the upper part of the Coralline zone, Trochus ziziphinus, &c., abound in individuals on the English shores. Between 25 and 40 fathoms, in the middle and lower sections of the Coralline region, the species observed most prolific in individuals on the English coast were few, comprehending Solen pellucidus, Pecten varius, Modiola modiolus, and Dentalium tarentinum.

On the Scottish coast this region is remarkable for prolific and peculiar species. Great numbers of Brachiopoda (Terebratula Caput-serpentis, and Crania norvegica) are found in gravelly and stony places. Dentalium entalis, Nucula nucleus, Astarte sulcata, Leda caudata, and (in places) L. pygmæa, Mactra elliptica, and Modiola modiolus, are all very prolific.

Between 40 and 60 fathoms, on the verge of the region of deepsea corals, we have too little experience on the English coast to judge. Cardium suecicum, however, essentially a northern form, was noted as abundant at a depth of 50 fathoms between Cornwall and Ireland.

In the Scottish seas between these depths, besides most of the species noted as prolific in the last region, we find Nucula tenuis, Cardium suecicum, Nucula decussata (locally), and Venus fasciata abundant; also, Turritella in places. Below that depth, Leda caudata, Syndosmya intermedia, Venus ovata and striatula (var.), Lucina spinifera, Dentalium entalis, Turritella, Ditrupa, and Echinus norvegicus, have been taken in considerable numbers in several Scottish localities. Widely diffused species of Turritella, Dentalium, Modiola, Nucula, Venus, and Astarte, appear to be most prolific throughout the range of their distribution.

Generic and subgeneric groups confined to particular zones in depth. In the Littoral and Laminarian zones, we find all the species of certain well marked natural groups assembled, but very few, if any, of those which are distributed in the regions of corallines and of deep-sea corals are peculiar, the species of mollusks, in the lower zones especially, being members of genera which have represen

tatives in the Laminarian or in both Littoral and Laminarian zones.

Relation of colour to distribution.-Although the extent and depth of our seas scarcely afford sufficient data for illustrating the influence of light in the colouring of marine animals, yet some facts bearing on this subject may be gathered from the papers before us. In the horizontal diffusion of species, several, as some of the Trochi and Venerida, exhibit a distinct influence of light upon the brightness of their hues, in the south, as compared with the dull aspect of specimens from the north, and this in individuals of the same species. It is easy for the practised conchologist to distinguish specimens of most painted shells, gathered on the southern coasts of England, from those taken on other parts of our shores. We have evidence

also of the distinct effect of depth in the defacing of the hues of the same species, when it has a great bathymetrical range. Thus, the examples of Venus striatula, Venus ovata, and Turritella terebra (all having a range from the Laminarian zone to the deepest recesses of the British seas), taken alive at a depth of 100 fathoms off the Zetland Isles by Mr MacAndrew, were colourless; whilst those from more moderate and shallow depths are almost always conspicuously coloured. Between 60 and 80 fathoms in the Scottish seas, dirty white, dull red, yellow or brown, rarely broken into stripes or bands, are the prevailing hues of the testacea; though at 50 fathoms, shells painted in patterns and vividly coloured (as Natica Alderi and Clavatula purpurea), exhibit their hues unimpaired. At the same time it must not be forgotten that the vividly painted animal of the coral Caryophyllia thrives at a depth of 80 fathoms. curious phenomenon apparently connected with depth is the blindness of the crustacean Calocaris.

Condition of the exuviæ of marine invertebrata taken in the dredge. -In the great majority of instances and places, the dead shells of mollusca are taken nearly entire, or, in the case of the bivalves, with the valves disunited but not broken. This applies especially to all localities of a considerable depth, and where strong currents are not in action. Very near the shore, broken shells are not uncommon; and in current-ways, even at the depth of 30 fathoms, the bottom may be composed in great part of triturated shells. Lieut. Thomas, R.N., observes, when communicating his lists of Testacea dredged around the Orkney Islands, that "between Fair Island and the Orkneys, the bottom near the latter islands is either rocky or composed of large pieces of Modiola modiolus or Pectunculus glycimeris. I make no doubt," he remarks "that these are broken by some large species of Crustacea (?); their freshness of fracture is astonishing, as if the creature feeding had been disturbed at his meal." Among bivalves, besides those mentioned, the shells of Thracia, Cyprina, Isocardia, and the larger species of Cardium, are most frequently found broken; among univalves, those of Buccinum and Fusus. Some few bivalves are frequently dredged dead, yet with their valves united; such are Lucina radula, the Neære, Mactra elliptica, Psammobiæ, Venus ovata and striatula, Tapes virginea, Tellina donacina, Thracia phaseolina, Lucinopsis, Nucula pygmæa, Solens, Syndosmya, and Pectunculus pilosus, this last open and gaping. The monomyarious bivalves are often found dead in quantities, but almost always with valves disunited; and this may be said of the great majority of dimyarious bivalves also. Echinoderms fall to pieces when dead, or if taken entire have lost their spines.

Phenomena of the horizontal distribution of species on the western shores of Great Britain.-In the older accounts of British marine animals, the phrase "from Devon to Zetland" was frequently given as marking their range, and the natural inference from such