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• W2281285909 abstract "Having in possession several slides of this diatom presented me through the kind liberality of Mr. Harrison and George Norman Esq., of Hull, containing entire shells and fragments of exquisite beauty, some of which constitute part of a gathering obtained from seaweed direct from the hands of the late Professor Bailey (Harrison), and having examined my entire stock with all care and attention, and under varied modes of manipulation, reversing the slides, and thus obtaining several aspects of each particular shell, so necessary in the examination of all fine and complicated striation, having also referred to Professor Bailey’s published plates (‘Smithsonian Contributions,’ vol. vii, Feb., 1854), furnished me by Mr. Harrison, as well also to my subscription copy of Pritchard’s ‘Infusoria,’ plate v, fig, 60, both these latter being magnified by a hand lens of to 1 inch focus, I find circumstances attending the subject which appear worthy of a more extended inquiry, and to merit a rigid examination by more able and experienced microscopists than myself, who may possibly possess specimens more favorable for conclusive interpretation, than such as with the few materials I have at command, I am alone able to submit on the present occasion.Dr. Bailey figures Hyalodiscus subtilis with three sets of striation, id est, one set radiating, and two others of contrary curvilinear description, the three sets collectively and their several intersections constituting a most rare, elaborate, and beauteous design.Neither Bailey nor Pritchard represent any striation over the central umbilicus, but figure this portion as being merely coarsely granular, whereas I would direct more particular attention to the varied appearance of this central part under different foci and illumination, as an index to the entire phenomena throughout the disc, for just as striation is seen upon the umbilicus, whether radiating or curvilinear, so does it prove, on closer examination, indicative of the course or direction of striation found upon the outer border, and it is in a measure the varied intersections upon this part, which at times yields a comparative coarse and confused granular aspect, although the central and exterior markings will be ultimately found to be continuous, or prolongations one of the other.The granular condition of the umbilicus contrasted with its superficial striation, would in some instances, seem to constitute a substratum; a granular condition being also frequently found to pervade the entire shell, as if arising from some abnormal development, or as having been subjected to some accidental or extraneous agency; and it is much this condition of things so frequently existing amidst these productions from certain localities, which detracts so greatly from the beauty of structure, and lessens interest attached to this peculiar diatom, or otherwise there exists other species not exhibiting the curvilinear markings of Professor Bailey.— A matter of no little importance suggests itself; do the figures represented by Bailey and Pritchard refer to the entire group of lines with their several intersections as capable of being seen under the objective simultaneously, at any one given portion of the shell, or merely as being in part and variously developed on several different portions, thus rendering it necessary, ideally to build up, by collecting or associating such diversified representations to constitute a whole ? For my own part, I have not hitherto been enabled to resolve the threefold delineation completing the figure at any single point at one and the same moment, that is to say, the two diverging (decussating) and the radiating lines one and all simultaneously intersecting; but have always occasion to resort to the expedient of revolving the slide so as to present the object under different aspects relative to illumination, whereupon alone I have succeeded in obtaining a striation complimental to that previously exhibited only in part, and then with a field of decussation or intersection but limited in degree.When surveying an entire shell, well calculated for observation, the following characteristic features present themselves, —the two decussating and diverging portions of the threefold series of lines are to be found ONLY in the direction of the axis of illumination, and also at the opposite extremity of the said axis, while the radiating portion of the series will be found at either extremity of a line at right angles to the foregoing, (id est), that each alternate quadrant of the circle is the seat of decussating or otherwise radiating portions of the series, the decussating always being on the line of axis of illumination, and the radiating at right angles to these, and upon revolving the slide through an arc of 90 degrees, the previous radiating now become decussating, and the previously decussating now become radiating, and so ringing the changes throughout the disc; the same phenomena are consequent upon manipulation with any fragment howsoever, possessing a readily visible striation, as well as upon the entire shell; indeed, for ordinary observation, I have found some fragments of greatest interest,—upon two or three of which in my possession the markings are so vividly displayed through peculiarity of shell structure, that with a Dallmeyer’s inch objective of 165° angle of aperture, I am easily enabled to command any measure of amplification of the same, within the limit of four thousand diameters, (id est, 120 × by 30 (eye-piece objective) = 3·600 + axis extension = 4000, a fact which I hereby employ to signify the value and brilliancy of the shells in question, concluding hence that with choice of such a range of magnitude and distinction, every existing feature ought to be fully and fairly elicited,—somewhat warranting the conviction, that the previous representations of authors are exaggerated; and whatever may constitute the normal shell structure, the direction of illumination plays no unimportant part in the display of varied phenomena; nevertheless, there exists undoubted beauty, well worthy of the keenest research. Radiating lines, if these were uninterruptedly continuous from the centre to the circumference, they must necessarily diverge, and produce wider interspaces towards the border of the shell, which is not apparently the case; for some specimens exhibit a peculiar mottled appearance, occasioned probably (as seen evidently on other discoidal diatoms) by the insertion of other shorter lines, shortening still as their successive insertions approach the periphery, thus presenting a series of zones, and so occasioning the markings at the periphery in point of measure or numerical value, to be about the average or mean of these obtained on other more central portions of the disc, the value of which I have estimated at about 66 to 70 in ·001″, or much about the same as obtained on Pleurosigma makrum, chiefly by white cloud illumination.Professor Bailey gives the relative proportion of the umbilicus of Hyalodiscus subtilis as being about one third the diameter of the entire disc. I hence subjoin a series of measures which may possess some share of utility, although great variations are found to exist.Hyalodiscus subtilis and its Associates, &C,Upon Four Shells of each Slide.It hence appears that Hyalodiscus subtilis by no means uniformly possesses an umbilicus, as formerly stated, at about one third that of the entire disc, and so far as relative proportion goes, can form no distinguishing feature from Hyalod. lœvis, said to be about one half, see slides, 3, 4, 5, 6, 8; and that as regards a fracture-like insertion of the umbilicus, a reputed characteristic feature of Hyalod. lœvis also, such insertion is found likewise in slides No. 3 and 7 specimens of Yarra Yarra, these are matters, therefore, for future consideration, being hitherto too speculative according to present observation.The slides most remarkable for clear and well-defined markings are Nos. 2 and 8, which I most highly prize. I cannot, however, record the associates of No. 2, being picked out specimens, but whomsoever may possess, or be enabled to obtain Hyalodiscus subtilis, Californian specimen, associated with Biddulphia Roperi, and Aulacodiscus oreganis, as per slide No. 8, may account himself fortunate, and will find therein ample field for exercise both mental and manipulative, and in the end discover it hardly possible to lay the subject aside, without contemplating for what purpose the Supreme Architect of Nature builds up such inconceivably minute forms, in such vast abundance, so widely diffused, and with such superb embroidery, and yet to be almost beyond human gaze with all the resources and appliances of modern art at command. Do the lower existences behold these hidden gems, and wonder and give praise ?p. s. I must state, also, that I have satisfactorily seen the decussations &c., upon No. 4 slide, and also upon an additional slide.No. 9, Californian, associated with Rhizosolenia." @default.
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• W2281285909 date "1861-07-01" @default.
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• W2281285909 title "On Hyalodiscus subtilis (Syn. Craspedodiscus Franklini)" @default.
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