Excerpt from An Atlas of the Fertilization and Karyokinesis of the Ovum

IT is the object of this work to place before teachers and students of biology a series of figures, photographed directly from nature, to illustrate some of the principal phenomena in the fertilization and early development of the animal ovum. In no branch of biological inquiry has knowledge advanced of late with such rapid strides as in the new science of cytology, which deals with the internal phenomena of cell-life. Within the past two decades this science has brought forward discoveries relating to the fertilization of the egg and the closely related subjects of cell-division and karyokinesis that have called forth, on the part of W'eismann and others, some of the most important and suggestive discussions of the post-darwinian biology. These discoveries must in some measure be dealt with by every modern text-book of morphology or physiology, yet they belong to a region of observation inaccessible to the general reader or student, since it can only be approached by means of a refined histological technique applied to special objects not ordinarily available for practical study or demonstration. A knowledge of the subject must, therefore, as a rule, be acquired from text-books in which drawings are made to take the place of the real object.

But no drawing, however excellent, can convey an accurate mental picture of the real object. It is extremely difficult for even the most skilful draughtsman to represent the exact appearance of protoplasm and of the delicate and complicated apparatus of the cell. The best drawing must necessarily be in some measure schematic and embodies a considerable subjective element of interpretation; it is, moreover, impossible adequately to reproduce it in a black and white text-book figure. The photograph, whatever be its shortcomings (and no photograph can do full justice to nature), at least gives an absolutely unbiassed representation of what appears under the microscope; it contains no subjective element, save that involved in focussing the instrument, and hence conveys a true mental picture. Even a technically perfect photograph, however, is defective in that it sharply reproduces only what is seen at a single level of the focus. In using high powers, moreover, the sharp image at the exact focus is always blurred to some extent by indistinct images of higher and lower levels, and this is the case with even the thinnest sections. Protoplasm is thus made to appear in the photograph more coarsely granular than it does to the eye, the asters are less sharp and brilliant, the apparent size of chromosomes and other minute bodies may be slightly exaggerated, etc. Nevertheless, on the whole, these unavoidable defects of the photograph introduce negative rather than positive errors, - they are faults of omission rather than commission, - and I believe that the photographic plates here presented give, on the whole, a clear and accurate impres sion of the preparations.

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