4 Rickett.—Fertilization in Sphaerocarpos. 237 
Targionia as having a denser zone of cytoplasm surrounding the nucleus. 
Miss Graham (1918) reports that the outer zone of the egg of Preissia is 
more coarsely alveolar than the portion around the pronuclei. In Nephro- 
dinm , according to Yamanouchi (1908), the cytoplasm of the egg has 
a finely fibrillar structure, very dense about the nucleus and vacuolate 
towards the periphery. 
It is of course impossible to draw from fixed material any final con¬ 
clusion as to the actual structure of the protoplasm in the living state. But 
since the stages herein described were all seen in preparations made in 
exactly the same way, with the same reagents, and since, as will be seen, 
there is a progressive series of changes in the cytoplasm, it is evident that, 
if not the structure, at least the substance, of the cytoplasm must undergo 
changes during the process of fertilization. The whole series of changes 
lends support to the idea that there are two kinds of substance present in 
the cytoplasm, corresponding perhaps to Strasburger’s (1892, 1893) ‘ tropho- 
plasm ’ and c kinoplasm ’, which at first are uniformly distributed throughout 
the cytoplasm, but of which one later becomes more or less localized and 
differentiated for its special functions. 
Eggs observed at this stage measured about 50 by 20 /x. The average 
difference in length (10 jm) between these eggs and mature unfertilized eggs 
is probably significant, and indicates that the egg begins to enlarge at this 
time. This is in accordance with the account of Garber (1904) for Riccia 
naians , and of Campbell (1918) for Riccia glatica (?), both of whom described 
the egg as enlarging immediately after fertilization. 
The female nucleus is also larger than that of the unfertilized egg, 
measuring about 17 by 12 /jl. Its structure is essentially that already 
described. Fig. 2 shows an egg whose nucleus, although the antherozoid 
has already entered, contains traces of chromosomes which have persisted 
from the last preceding division. Usually, however, the egg nucleus has 
rather the appearance shown in Figs. 4 and 5 , containing numerous small, 
irregular masses, granules, and rods, some scattered through the nuclear 
cavity, but most of them massed in the centre about the large nucleolus and 
almost hiding it. The nucleoli, of which there may be one or two, often 
appear irregular in shape, but this is probably due to the fact that masses 
of chromatin are grouped about and in contact with them. 
There is no definite relation between the respective positions of the male 
and female nuclei. Just as, apparently, the antherozoid may penetrate the 
egg at any point, the male nucleus may lie in any part of the cytoplasm, and 
at any relative distance from the plasma membrane and from the nucleus of 
the egg. Most frequently the male nucleus is somewhat towards the distal 
end of the egg, and about midway between the egg nucleus and the outer 
boundary of the cytoplasm. 
This phase extends through about two hours from the time of flooding. 
