12 



collaris, Fig. 7, is considerably larger than the male gamete). The 

 cell in which the gametes are developed is called a gametangium, 

 and the reproductive cell formed by their union which generally 



has a thick wall and only 

 germinates after a short 

 period of rest is termed a 

 zygote or zygnspore. The con- 

 jugation takes place in two 

 ways : 



(a) In the one way the 

 gametes are motile cells 

 ( planogametes, zoogametes, 

 Fig. 8), which unite in 

 pairs during their swarming 

 hither and thither in the 

 water ; during this process 

 they lie side by side (Fig. 8d), 

 generally at first touching at 

 the clear anterior end, and 

 after a time they coalesce 

 and become a motionless zy- 

 gote, which surrounds itself 

 with a cell-wall (Fig. 8 e). 

 This form of conjugation is found in Ulothrix (Fig. 8 d), Acetdbu- 

 laria, and other Algae (Figs. 45, 56, 66). 



(6) Among other Algae (e.g. Diatomacece and Conjugatce), the 

 conjugating cells continue to be surrounded by the cell -wall of 

 the mother-cell (aplanogametes in an aplanogametangiuin) ; the 



FIG. 7. Zanardinia collaris. A Male game- 

 tangia (the small-celled) and female gametangia 

 (large-celled). C Female gamete. D Male gamete. 

 B E Fertilisation. F Zygote. G Germinating 

 zygote. 



FIG. 8. Ulothrix zonata : a portion of a thread with zoospores, of which two are formed 

 in each cell (zoosporangium), the dark spots upon them are the "red eye-spots " ; 1, 2, 3, 

 4 depict successive stages in the development of the zoospores ; b a single zoospore, at v 

 the pulsating vacuole ; c portion of a thread with gametes, of which sixteen are formed in 

 each gametangium ; d gametes free and in conjugation; e conjugation has been effected, 

 and the formed zygotes are in the resting condition. 



