522 Reproduction in Fresh- Water Alge. — [ September, 
which produce asexual, that is, swarm-spore-forming plants, from 
which similar ones proceed, until the series of them is closed by a 
sexual generation (with formation of odspores); but the sexual 
plants produce swarm-spores as well. ‘The sexual plants are 
either moneecious or dicecious: in many species the female plant 
produces peculiar swarm-spores, out of which proceed very small 
male plants (dwarf males). The swarm-spore is developed in an 
ordinary cell of the filaments by the contraction of its whole pro- 
toplasmic substance (Figure 93, a); it becomes free from the 
“Se 
(Fic, 93.) CEDOGONIUM. 
mother-cell, the cell-wall splitting by a transverse slit into two 
very unequal parts. The swarm-spore is encircled at its hyaline 
end—the anterior end during swarming — by a crest of nu- 
merous cilia. The spermatozoids are very similar in form to the 
swarm-spores, but much smaller (b, b); their motion, due to # 
crest of cilia, is also less. The androspores, from which the dwarf 
male plants arise, are produced from mother-cells similar to those 
which give birth to the spermatozoids. After swarming they as 
themselves to a definite part of the female plant, on or near g 
oögonium, and after germination produce at once the antheridium- 
