Page:Proceedings of the Royal Society of London Vol 60.djvu/213

Rh S eries II.—Observations on Ascophyllum carried on the Laboratory.

Antherozoids added between 5 and 7 p.m. Lot 1. Fixed 22} hours after the addition of antherozoids. Nucleus divided, no rhizoid or dividing wall. . „ 2. „ 23 „ „ „ Nucleus preparing for division. „ 3. „ 23 „ „ „ Same as 1. „ 4. „ 24f „ ,, „ Nucleus divided, rhizoid present, no dividing wall.

The above observations prove that there is no essential difference between the behaviour of material examined in London and at the seaside respectively.

After fertilisation, the cells rest for a long interval of time—commonly about twenty-four hours, as shown in the foregoing table— before they begin to segment. The principal changes which occur during the interval are, first, in the rapid increase in the thickness of the peripheral cell wall, and, secondly, in the more regular arrangement of structure exhibited by the protoplasm. The alveolar, or foam character is extremely clear, and the chromatophores, which by this time have become very prominent, are noticed to be situated in the angles formed by the convergence of the foam walls; they are often bent and otherwise distorted, and so accommodate themselves to the structural condition of the foam. Other granules, which stain deeply, and probably represent food reserve of a proteid nature, are also abundantly scattered through the cytoplasm.

The first segmentation-division resembles, in a general way, the oogonial nuclear divisions already described, and the polar areas become similarly cleared of granules. The achromatic threads forming the polar radiations are very clearly seen to be attached to the foam-like structure of the cytoplasm, and, indeed, in some cases, insensibly to pass into it. At other times fibrils end on granules (or, pci haps, on the protoplasmic lining of the granules), and sometimes again a fibril may fork, and its branches end either on granules or on the foam angles. The inference to be drawn from these facts seems to be that the radiations are the result of a change—a differentiation in the protoplasm as it already exists, and that they do not owe their origin to the presence of any special “ spindle-forming substance, ^ by virtue of which they may be supposed to develop and grow as new structures in the cell. We propose, however, to discuss the general bearings of our observations on this and on other questions of theoretical interest in a future memoir, in which the evidence for our views will be set forth in detail.

When the achromatic nuclear spindle appears, it also, as in the