236 THE AMERICAN NATURALIST. Vor. XXXIX. 
The sperm of Fucus upon entering the egg loses its cytoplasm 
and passes rapidly to the egg nucleus as a deeply staining body 
resembling a plastid in form. This structure is the male nucleus 
whose chromatin is so densely crowded that it stains too deeply 
to show much structure. Arriving at the side of the female 
nucleus, about ten minutes after its entrance into the egg, the 
male nucleus flattens against the female and increases in size so 
that the chromatin appears less condensed. The male nucleus 
is then absorbed so that the paternal chromatin lies within a 
fusion nucleus but may be distinguished for some time as 
densely staining material at one side. A second nucleolus 
often appears in the fusion nucleus in the vicinity of the pater- 
nal chromatin and is probably associated with the entrance of 
the sperm nucleus, although it is not likely to have been brought 
in as an organized structure but developed later at the expense 
of material in the sperm nucleus. The fusion nucleus remains 
quiescent for from 20 to 24 hours during which time the paternal 
' chromatin becomes so distributed that it can no longer be fol- 
lowed. Then two centrospheres with conspicuous radiations 
appear at opposite poles of the fusion nucleus and the first 
cleavage spindle is organized. There is no evidence that either 
of these centrospheres is brought into the egg by the sperm and 
both appear de novo and independently of one another. 
The chief accounts of the fusion of gamete nuclei in thallo- 
phytes are as follows: Closterium and Cosmarium (Klebahn, 
'91); Rhopalodia (Klebahn, '906); Cocconeis (Karsten, :00); 
Sphaeroplea (Klebahn, '99; Golenkin, '99); CEdogonium (Kle- 
bahn, '92); Coleochzeta (Oltmanns, '98); Vaucheria (Oltmanns, 
'95; Davis, :04); Fucus (Strasburger, '97a; Farmer and 
Williams, '98); Batrachospermum (Schmidle, '99; Osterhout, 
:00); Nemalion (Wolfe, :04); Basidiobolus (Fairchild, '97); 
Albugo (Wager, ’96; Stevens, ’99,:01b; Davis, :00) ; Perono- 
spora (Wager, :00); Pythium (Miyake, :01 ; Trow, :01); Ach- 
lya (Trow, :04) ; Araiospora (King, :03); Sphzerotheca (Harper, 
'95); Pyronema (Harper, :00). Most of these papers with 
others on fertilization in the thallophytes are summarized by 
Mottier, (:04 b) in very convenient form for reference. 
There is some confusion in the accounts of fertilization in 
