The origin and nature of meroblastic ova will best be understood by taking an ovum with an unequal segmentation, such as that of the frog, and considering what would take place in accordance with the laws already laid down, supposing the amount of food-yolk at the vitelline pole to be enormously increased. What would happen may be conveniently illustrated by fig. 44, representing the segmentation of a fowl's egg. There would first obviously appear a vertical furrow at the formative or protoplasmic pole. (Fig. 44 A, _b_.) This would gradually advance round the ovum and commence to divide it into two halves. Before the furrow had however proceeded very far it would come to the vitelline part of the ovum; here, according to the law previously enunciated, it would travel very slowly, and if the amount of the food-yolk was practically infinite as compared with the protoplasm, it would absolutely cease to advance. A second vertical furrow would soon be formed, crossing the first at right angles, and like it not advancing beyond the edge of the germinal disc. (Fig. 44 B.) The next furrow should be an equatorial one (as a matter of fact in the fowl's ovum an equatorial furrow is not formed till after two more vertical furrows have appeared). The equatorial furrow would however, in accordance with the analogy of the frog, _not be formed at the equator, but very close to the formative pole_. It would therefore separate off as a distinct segment (fig. 44 C, _c_), a small central, _i.e._ polar, portion of each of the imperfect segments formed by the previous vertical furrows. By a continuation of the process of segmentation, with the same alternation of vertical and equatorial furrows as in the frog, a cap or disc of small segments would obviously be formed at the protoplasmic pole of the ovum, outside which would be a number of deep radiating grooves (fig. 45), formed by the vertical furrows, the advance of which round the ovum has come to an end owing to the too great proportion of yolk spheres at the vitelline pole. [FIG. 45. SURFACE VIEW OF THE GERMINAL DISC OF FOWL'S EGG DURING A LATE STAGE OF THE SEGMENTATION. _c._ small central segmentation spheres; _b._ larger segments outside these; _a._ large, imperfectly circumscribed, marginal segments; _e._ margin of germinal disc.] It is clear from the above that an immense accumulation of food-yolk at the vitelline pole necessarily causes a partial segmentation. It is equally clear that the part of meroblastic ova which does not undergo segmentation is not a new addition absent in other cases. It is on the contrary to be regarded merely as a part of the ovum in which the yolk-spherules have attained to a very great bulk as compared with the protoplasm; sometimes even to the complete exclusion of the protoplasm.