On Fertilisation, and the Segmentation of the Spore in Fucus. 191 



were really ten or twelve, but the absolute number is not of im- 

 portance as all the nuclei were compared from the same aspect. 

 Remains, more or less preserving the original form, of the nucleolus 

 were sometimes visible at this and even in a later stage. No division- 

 planes are formed in the oogonium until the full complement of nuclei 

 are produced; after this the positions which they will ultimately 

 occupy are indicated by the heaping up into lines (or rather plates) 

 of the cytoplasmic granules above referred to. These seem to be 

 repelled equally from all the nuclei, thus effecting a symmetrical 

 division of the entire oogonium. 



After the complete delimitation of the oospheres within the 

 oogonium, we observed, as an occasional circumstance, that one of 

 the oospheres might contain two, or even three, nuclei, a fact also 

 noticed by Oltmanns. When the oospheres are extruded, and come 

 to lie free in the water, they grow in size, and are turbid with granules, 

 which are very abundant in the cytoplasm. The chromatophores 

 early become distinguishable from the other constituents of the cell, 

 and the nucleus occupies a central position. It is itself sur- 

 rounded by a dense layer of cytoplasm, which later on becomes 

 very strongly marked. About five minutes after the mixing of the 

 sexual cells, the antherozoids are found to have slipped into many of 

 the oospheres. We failed to observe the act of penetration, but found 

 a number of cases in which the antherozoid could be recognised 

 within the oosphere, before its final fusion with the nucleus of the 

 latter. It is a roundish, densely staining body, and, unlike the majo- 

 rity of animal sperm cells as yet described, it imports into the egg no 

 system of radiations along with it. Judging from the short period 

 of time elapsing between its penetration of the surface of the oosphere 

 and its arrival at the exterior of the female nucleus, it must pass 

 through the intervening cytoplasm with great rapidity. It then 

 becomes closely appressed to the nucleus, and is about as large as the 

 nucleolus of the latter. It rapidly spreads over a part of the female 

 nucleus as a cap, and it presents a less homogeneous aspect than 

 before. Both it and the female nucleus assume a granular condition, 

 which is probably to be interpreted as representing a coiling and 

 looping of the lining of the respective nuclei. Finally the two nuclei 

 coalesce, and the original components can no longer be distinguished. 

 Complete fusion may be effected in less than ten minutes after 

 addition of the antherozoids to the water. These results are in 

 striking accordance with those described by Wilson in connexion 

 with the fertilisation of the eggs of echinoderms in his recent " Atlas 

 of Fertilisation." 



A delicate pellicle is meanwhile formed around the periphery of 

 the oosphere, which is thus easily distinguished from the unfertilised 

 oospheres, in which such a membrane is wanting. The texture of the 



