SYNGAMY 



227 



more active ones become attached by a cilium to the anchored ones and 

 gradually undergo fusion with them (Fig. 138, B). The fusion culminates 

 in the union of the nuclei. In such gametic fusions the plastids undergo 

 no fusion, so far as is known. In some cases they have been followed 

 through into the new individual. In Fucus the large passive eggs and the 

 small motile spermatozoids are shed from the organs which bear them, 

 their union occurring in the sea water. Many spermatozoids attach 

 themselves to each egg by one cilium, but after one of them enters the egg 

 the others move away. The male nucleus remains relatively small up to 

 the time it fuses with the egg nucleus, and a centrosome with an aster 



Fig. 138. — Syngamy in various alga. A, gamete, union of similar gametes (isogamy), 

 and zygote of Ulothrix. B, isogamy in Ectocarpus siliculosus. (After Oltmanns, 1897.) 

 C, portion of filament of CEdogonium; spermatozoids escaping from antheridial cells below; 

 spermatozoid about to enter egg above. (After Coulter.) D, the formation of eggs by 

 subdivision of a ccpnocytic protoplast in Spharoplea. E, portion of filament of Sphceroplea 

 showing several eggs; spermatozoids have entered through pores in filament wall. (D and 

 E after Klehahn.) 



appears near the nuclear membrane at the point where the male nucleus 

 enters (Yamanouchi, 1909). This latter phenomenon, which is very 

 suggestive of what occurs in animals, has also been observed in Didyota 

 (J. Williams, 1904). 



In (Edogonium and Vaucheria the egg is not liberated from the 

 oogonium but is fertilized in situ by a spermatozoid. The latter passes 

 into the oogonium through a specially differentiated pore and then enters 

 the egg at a more or less distinct receptive spot. In the mature male 

 gametes of Vaucheria, Chara, and Coleochcete no plastids have been demon- 

 strated, the new individual apparently deriving these organs wholly from 

 the female gamete. This statement, however, may require revision when 

 male gametes have been more fully studied with methods specially devised 

 for the investigation of cytoplasmic differentiations. In Polysiphonia the 

 non-motile male gamete (spermatium) comes in contact with a prolonga- 



