236 THE AMERICAN NATURALIST. [Vol. XXXIX. 



The sperm of Fucus upon entering the ^gg 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 ilattens 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, '96) ; Cocconeis (Karsten, : 00) ; 

 Sphaeroplea (Klebahn, '99 ; Golenkin, '99) ; CEdogonium (Kle- 

 bahn, '92) ; Coleochaeta (Oltmanns, '98) ; Vaucheria (Oltraanns, 

 '95 ; Davis, : 04) ; Fucus (Strasburger, '97 a ; Farmer and 

 Williams, '98) ; Batrachospermum (Schmidle, '99 ; Osterhout, 

 : 00) ; Nemalion (Wolfe, : 04) ; Basidiobolus (Fairchild, '97) ; 

 Albugo (Wager, '96; Stevens, '99, :oib; Davis, :oo); Perono- 

 spora (Wager, :oo); Pythium (Miyake, :oi ; Trow, :oi); Ach- 

 lya (Trow, : 04) ; Araiospora (King, : 03) ; Sphaerotheca (Harper, 

 '95); Pyronema (Harper, :oo). 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 



