Rickett.—Fertilization in Sphaerocarpos . 227 
reported for any other Liverwort. He figures a cross-section of the aiche- 
■ gonium and egg, with the antherozoid, a long, thin, curved body, lying 
in the egg cytoplasm, with one end in contact with the egg nucleus. This 
; antherozoid resembles the free-swimming cell, and has no lesemblance 
to a resting nucleus, or even to the antherozoid immediately aftei its 
entrance into the egg as described by Kruch and by the present writer. 
Humphrey reported that the egg of Fossombvonia has a well-defined recep¬ 
tive spot, but did not describe the latter. He described the large egg 
nucleus as possessing but one nucleolus and a small amount ot chromatin. 
Meyer (1911) obtained several fertilization stages in Corsinia mar chan- 
tioides , which showed the male and female nuclei lying side by side in the 
egg cytoplasm. In the earliest stages observed, the male nucleus has alieady 
rounded up and is surrounded by a clearly defined membrane. In its centre 
is a small mass of chromatin granules, from which linin thieads extend 
towards the periphery. Later the chromatin granules become spread 
throughout the nucleus, which is now filled with a complicated fine netwoik. 
The large egg nucleus is similar in structure. The cytoplasm of the egg is 
quite dense, and filled with vacuoles which are arranged somewhat radially 
about the nucleus as a centre. The egg was somewhat shrunken undei the 
influence of the fixing fluid, and was surrounded by a cleaily defined 
fertilization membrane after the entrance of the antherozoid. 
Miss Black (1913) saw one stage in Riccia Frostii similar to that just 
described for Corsinia . The male nucleus lay in the egg cytoplasm beside 
the egg nucleus. Its structure was that of a resting nucleus, She also 
figures one egg which she interprets as having been fertilized and in which 
the nuclei have already fused. Its nucleus is large, and the chromatin 
is collected in a cord or in short segments, with a fine network occupying 
the remaining space. This, she says, is typical of a great number of eggs 
observed. She also reports the division, after the entrance of the anthero¬ 
zoid, of the cells that make up the wall of the venter—the basal cells usually 
dividing first. 
Miss Graham (1918) figured male and female nuclei in the cytoplasm of 
the egg of Preissia quadrata. The male nucleus is smaller than the female. 
The chromatin in both is massed in the centre of the nucleus, and seems to 
be in the form of small masses or rods.. She was chiefly inteiested in the 
discovery of centrosomes in the egg during fertilization, to which refer¬ 
ence will be made in another connexion. 
Woodburn (1920) shows one stage in fertilization in Reboulia hemi- 
sphaerica , which is general is similar to those just described. The nuclei 
are stated to be in the resting condition, though the figure is not 
very clear. 
Sharpe (1921) figures one stage in the fertilization of Anthoceros. The 
male nucleus lies within the egg cytoplasm, in contact with the egg nucleus. 
