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132 stance diminishes in quantity, the muscular fibres lie closer together, and have a more intensely white appearance upon the black ground. When some of this transparent substance, taken from a foetus of the size before mentioned (and in order to exclude as completely as possible the embryonal cellular tissue which surrounds the entire muscle, a portion should be cut out from the centre of the muscle), is examined with a magnifying power of 450, it exhibits various kinds of granules differing m size, and lying in a finely granulous mass. On examining these granules more accurately, they are found to vary, both in size and appearance, being round or oval, more or less opaque or transparent. A great many of them may be recognized as cell-nuclei by their form. In many instances, even when they are still connected together, the granulous substance around them is more or less distinctly seen to have a defined globular figure, within which the nucleus lies. This is, however, observed most distinctly when any of the granules become separated from the transparent substance, and float about in the fluid upon the object-glass. A quantity of globules are then seen floating about isolated, each one containing the characteristic cell-nucleus, which is placed eccentrical, varies much as to its size, and is often furnished with nucleoli. (See pl. III, fig. 18.) We are already familiar with this as the rudimentary form of most cells. The finely granulous portion of the transparent mass is formed, in part, of the bodies of the cells, which, when in close contact, are difficult to distin- guish, and in part, of the cytoblastema in which the cells have been generated. Some of these cells which float about are becoming elongated into fibres, which are manifestly those of areolar tissue. Such instances, however, are rare, and these cells seem to be something quite peculiar. They might be regarded as the primitive cells of new muscular fibres; but from the manner in which Valentin expresses himself, one should infer that they are formed at a later period, for he says, “masses of globules begin to accumulate between the muscular fasciculi from the period at which they become transparent;” it is clear that he here refers to the nuclei of these cells. This must, therefore, remain an undecided point.

We next examine the muscular fibres (primitive fasciculi) in the dorsal muscles of the same foetus. They do not all