12 



ALG.S. 



collaris, Fig. 7, is considei^ably larger than the male gamete). The 

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

 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 

 zyyote or sygospore. 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. 8tZ), 

 generally at first touching at 

 the clear anterior end, and 

 after a time they coalesce 

 and become a motionless zy- 

 fjote, which surrounds itself 

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

 This form of conjugation is found in Vlothrix (Fig. 8 d), Acetabu- 

 laria, and other Alga? (Figs. 45, 56, 66). 



(b) Among other Alga? (e.g. Diatomacece and Conjugates), the 

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

 the mother-cell (aplanogametes in an aplanogametanyinm] ; the 



G 



FIG. 7. Zannnlinia co'ilaris. A Male game- 

 tangia (the small-celled) and female gametangia 

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

 B E Fertilisation. F Zygote. G Germinating 

 zygote. 



\ 



FIB. 8. UlotUrlx zoiinta: 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 u 

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

 each g-ametangium ; d gametes free and in conjugation; e conjugation has been eSTected, 

 and the formed zygotes are in the resting condition. 



