. The cell; outlines of general anatomy and physiology. third is perpendicular to the two first, and passes through thecentre of the axis in which they intersect. If now the ends ofthis axis are considered as the poles of the egg, the two firstdivision planes may be regarded as meridional, and the third as-equatorial. In many cases, after the second cleavage, the four portions maybe seen to separate somewhat from one another, the result of which is that the furrows produced by the second division no longer intersect in one point, but meet the first formed meridional furrow at a little distance
. The cell; outlines of general anatomy and physiology. third is perpendicular to the two first, and passes through thecentre of the axis in which they intersect. If now the ends ofthis axis are considered as the poles of the egg, the two firstdivision planes may be regarded as meridional, and the third as-equatorial. In many cases, after the second cleavage, the four portions maybe seen to separate somewhat from one another, the result of which is that the furrows produced by the second division no longer intersect in one point, but meet the first formed meridional furrow at a little distance from the pole (Fig. 113). Thus a transverse line, the cleavage line, which varies in length, is produced. I have found this especially well marked (VI. 30b) in the eggs of Sagitta (Fig. 113). A short time after the termination Fig. 113. —a four segmented of the second division of the egg of egg of Sagitta seen from the Saqittci, the four cells so arrange them- animal pole, (x 160; Hertwig, ° Pi. v., Fig. 5.) selves (Fig. 113) that only two ot them. THE VITAL PHENOMENA OF THE CELL 225 touch each other. At the animal pole they meet in a short trans-verse farrow, the animal cleavage line. The pointed ends of thetwo remaining cells, which do not come in contact with the pole,meet this line at its extremities. A similar arrangement is seenat the vegetative pole : here the two cells, which did not touchthe animal pole, meet along a vegetative cleavage line, which isalways in such a position that if both lines were projected upona common plane they would intersect at right angles. Herethe four cells, which are obtained by quartering the originalcell, are not of the shape of ordinary quarters of a has a blunt and a pointed end, the latter being directedtowards the pole of the egg. Each pair ofcells formed from a hemisphere are so ar-ranged that similar ends point in oppositedirections. A corresponding arrangement of the firstfour cleavage cells has been described by von
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