416 Graham.—Centrosomes in Fertilization Stages 
described by Hertwig. And artificial astrospheres (cytasters), some with 
a clear centre, others with a granule on which rays centre, were observed 
by Wilson (1901) in the stimulated cytoplasm of unfertilized eggs of 
Toxopneustes variegatus. 
Central bodies and asters in the Algae are apparently related to cell and 
nuclear division in the same fashion as in animals. Radiations were observed 
by Farmer and Williams (1896-7) at opposite poles of the oogonial nucleus 
and also from the cleavage nucleus in Fucus vesiculosus ; and in the germina¬ 
tion of the oosphere of the same plant granules that stand at the centre of 
a ray system were observed by the same workers (1898). Two such systems 
are described as forming the poles of the fully formed spindle appearing 
during the prophases and persisting through the anaphases. Strasburger 
(1896-7) observed in F. serratus that two centrosomes with their radiations 
lie on the nuclear membrane of the fusion nucleus as it enters the anaphases. 
They lie on the margin of the fusion area of the two sexual nuclei, he points 
out, and form the poles of the fully formed spindle. Swingle (1897) 
observed fibres that radiate from definite small points at the poles of the 
nucleus in Stypocaulon. These systems, it is claimed, originate from a 
granule lying on the nuclear membrane; and kinoplasmic threads from the 
same centrosomes enter the nuclear cavity, become attached to the chromo¬ 
somes, and form the spindle. A rod-shaped centrosome on opposite poles 
of the nucleus and at the centre of diverging rays was observed in Dictyota 
dichofoma by Mottier (1900). Mottier also states that fibres penetrate the 
nuclear membrane and that some of them become attached to chromosomes. 
In the Fungi a relationship that exists between the chromatin and 
central body in Phyllactinia corytea during karyokinesis and the resting 
period was observed by Harper (1S05). In addition to this relation to 
division Harper observed that centrospheres are concerned with delimiting, 
the mass of cytoplasmic substance about the nucleus of the forming 
ascospore. 
The majority of recent authors, Hirase (1898), Belajeff (1899), Ikeno 
(1903), Chamberlain (1903), Jahn (1904), and Allen (191.2) seem to regard 
the blepharoplast as a modified central body. 
Farmer (1895) has described the centrospheres in the dividing spore 
mother-cell of Petlia epiphylla as arising at four points on the nuclear 
membrane, points from which radiations extend into the lobe nearest it. 
A minute centrosome was observed within the centrosphere. It is in the 
Bryophytes that we may expect to find clues to the explanation of the 
relations between the method of spindle formation in the higher plants 
where centrosomes are not present and the method of spindle formation in 
the Algae, Fungi, and animals where centrosomes are commonly present. 
There is considerable evidence that centrosomes are present in the vegetative 
divisions of the cells of Liverworts. In the germinating spore of Petlia 
