. Quain's elements of anatomy . ect, that there is in some sort a concentration ofthe process towards the germinal pole, where the cells resulting from the yolkcleavage are smaller and more numerous, while they become gradually largerand less distinctly separated towards the opposite or nutritive pole—a differencewhich is manifestly related to the* purer condition of the egg protoplasm in theneighbourhood of the first, which was the original seat of the germinal vesicle,and the larger quantity of nutritive yolk accumulated at the lower or anti-germinal pole. The accompanying diagram copied fro
. Quain's elements of anatomy . ect, that there is in some sort a concentration ofthe process towards the germinal pole, where the cells resulting from the yolkcleavage are smaller and more numerous, while they become gradually largerand less distinctly separated towards the opposite or nutritive pole—a differencewhich is manifestly related to the* purer condition of the egg protoplasm in theneighbourhood of the first, which was the original seat of the germinal vesicle,and the larger quantity of nutritive yolk accumulated at the lower or anti-germinal pole. The accompanying diagram copied from Ecker gives a sufficientlyclear view of the successive steps of the process ; 1 representing the undividedcondition, 2 the first vertical cleft which divides the whole yolk into two, 4indicates the stage at which by a second vertical cleft the yolk is now dividedinto four segments. In these two first stages the vertical clefts proceed down-wards from the upper or germinal pole, where they cross each other at right Fig. Fig. 629.—Unequal segmentation in the egg of the frog (from Balfour after Ecker.) Ten stages are represented ; the numbers over certain figures indicate the number ofsegments at each of these stages; in the intervening figures the fissures are in progress offormation. angles, to the lower or nutritive pole. In the next stage, however, marked 8, inwhich that number of segments have appeared, the new cleft is horizontal andparallel to the equator of the sphere, but at some distance above it. This againis succeeded by radial or meridional clefts which, proceeding gradually fi-om thegerminal pole, divide first the upper and later the lower segments, so as to pro-duce first twelve and later sixteen segments, as seen in the outline numbered equatorial clefts follow, which have the effect of dividing both the upperand lower meridional segments, so as to produce first 24 and subsequently 32segments; and by a succession of similar alternating vertical a
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