218 



duction in the conjugation of equivalent swarm-cells. Ulva produces 

 two kinds of swarm-spore megazoospores with four cilia, and micro- 



.^ob- * 

 jy^x 



'cgp^o^aoOQ' 



PQ^P^RQR 

 wSJ^y 



v^^^O^/r^ / 



FIG. 196. Ulva. 



a, portion of frond showing cells which produce the swarm-spores ; b, portion of 

 frond with empty cells ; c, megazoospores (magnified). 



zoospures or zoogametes with two cilia ; and 

 these two kinds are produced either on the same 

 or on different individuals. The megazoo- 

 spores germinate directly. Conjugation of the 

 smaller swarm-cells has been observed in Ulva, 

 Enteromorpha, and Monostroma, but the 

 coalescence takes place only gradually ; some 

 time after conjugation four cilia and two 

 pigment-spots are still to be detected. In 

 Ulva the zygosperm thus formed divides re- 

 peatedly after becoming attached to some solid 

 substance ; the cells thus formed separate, and 

 a small colony of multicellular individuals is 

 produced, each of which develops into a new 

 ' frond,' dividing first into a filament and then 

 into a plate. In Monostroma a non-sexual 

 mode of propagation has been observed. At 



FIG. 197. Enteromorpha intestinalis 

 Lk. (natural size). (After Hauck.) 



FIG. 198. Stages in the conjugation of the zoogametes 

 of Monostroma bullosiim Thur. (magnified). 



