Up to this period the processes in the different cells seem to have been controlled by the different character of the substance of each; but now it would seem that the changes become more independent of physical or material influences, for each kind of cell undergoes the same process.  They all assume the ordinary cell character, with outer and inner sac,—­the inner sac forming on the side, like the Purkinjean vesicle itself; but it does not retain this position, for, as soon as its wall is formed and it becomes a distinct body, it floats away from the side and takes its place in the centre.  Next there arise within it a number of little bodies crystalline in form, and which actually are wax or oil crystals.  They increase with great rapidity, the inner sac or mesoblast becoming sometimes so crowded with them, that its shape is affected by the protrusion of their angles.  This process goes on till all the cells are so filled by the mesoblast, with its myriad brood of cells, that the outer sac or ectoblast becomes a mere halo around it.  Then every mesoblast contracts; the contraction deepens, till it is divided across in both directions, separating thus into four parts, then into eight, then into sixteen, and so on, till every cell is crowded with hundreds of minute mesoblasts, each containing the indication of a central dot or entoblast.  At this period every yolk cell is itself like a whole yolk; for each cell is as full of lesser cells as the yolk-bag itself.

When the mesoblast has become thus infinitely subdivided into hundreds of minute spheres, the ectoblast bursts, and the new generations of cells thus set free collect in that part of the egg where the embryonic disk is to arise.  This process of segmentation continues to go on downward till the whole yolk is taken in.  These myriad cells are in fact the component parts of the little Turtle that is to be.  They will undergo certain modifications, to become flesh-cells, blood-cells, brain-cells, and so on, adapting themselves to the different organs they are to build up; but they have as much their definite and appointed share in the formation of the body now as at any later stage of its existence.

We are so accustomed to see life maintained through a variety of complicated organs that we are apt to think this the only way in which it can be manifested; and considering how closely life and the organs through which it is expressed are united, it is natural that we should believe them inseparably connected.  But embryological investigations have shown us that in the commencement none of these organs are formed, and yet that the principle of life is active, and that even after they exist, they cannot act, inclosed as they are.  In the little Chicken, for instance, before it is hatched, the lungs cannot breathe, for they are surrounded by fluid, the senses are inactive, for they receive no impressions from without, and all those functions establishing its relations with