This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1896. Not illustrated. Excerpt: ... and in others by the ovum only, it is not inconceivable that in yet other cases both may contribute to its formation. Therefore the observations of Guiguard and Conklin are not necessarily irreconcilable with those more recently made by "Wilson and Mathews, Mead, Wheeler, and myself, as well as the earlier observations of others. In any case, however, the theoretical conclusions based on Fol's "quadrille," as to the share which the attraction centres enjoy in the phenomena of heredity, may now be definitely set aside.1 V. POLARITY OF THE EGG. Attention has already been called to the fact that even before fertilization one axis of the egg, the vertical, has been determined. The point where the polar globules form is its dorsal pole, which lies at the centre of the surface of the less richly protoplasmic hemisphere. At some point on the surface of the opposite hemisphere, the spermatazoon usually enters the egg, and there is reason to believe that its point of entrance determines the median plane of the embryo, and so its antero-posterior axis. After the two pronuclei have met, they move toward the centre of the egg, and in that region the first cleavage spindle arises (Plate III. Fig. 14). It invariably lies parallel to a tangent at the point of formation of the polar globules. The first cleavage plane, which in accordance with a general law is perpendicular to the spindle at its equator, passes through the point where the polar globules arose and divides the egg into two equal blastomeres (Plate III. Fig. 15; cf. Plate V. Fig. 27). 1 Boveri ('95), in a paper recently received, completely confirms the observations of Wilson and Mathews regarding the source of the attractive bodies of the first cleavage spindle of the sea-urchin egg. He for the first time in his p...