On fertilisation, and the Segmentation of the Spore in Fucus. 193 



SERIES II. Observations on Ascophyllum carried on in the Laboratory. 

 Antherozoids added between 5 and 7 P.M. 



Lot 1. Fixed 22 hours after the addition of antherozoids. Nucleus divided, no rhi- 



zoid or dividing wall. 



2. 23 Nucleus preparing for 



division. 



3. 23 Same as 1. 



4. 24 ,, ,, 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 com- 

 monly 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 arrange- 

 ment 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 form- 

 ing 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, 

 perhaps, 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 differ- 

 entiation in the protoplasm as it already exists, and that they do not 

 owe their origin to the presence of any special " spindle-forming sub- 

 stance," 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 



