SEXUAL REPRODUCTION OF THALLOPHYTES. 305 
will be seen below, conjugation is now known to take place. 
Amongst the multicellular green alge (Nematophycee, 
See 
Fic. 2.—Conjugation of microzoospores of Cladophora glomerata x 500 
(after Cohn, 1. c., tab. xx, fig. 26). 
Rabh.) the formation of zygozoospores has recently been 
determined in a considerable number of species. 
Uornricuacem only differ from Confervacee in their 
filaments never branching and being composed of very 
short cells. ‘There seems to be no really valid ground for sepa- 
rating them in these respects. 
Hormiscia.—Cramer! discovered the conjugation of the 
microzoospores in 1870 in H. zonata, Web. and M. (Ulothrix 
zonata, Kutz.). Some cells of this species produce two 
to eight macrozoospores, others sixteen to thirty-two micro- 
zoospores. The details of conjugation agree in every respect 
with what Pringsheim has described in Pandorina. 
Urospora.—Areschoug” distinguishes this genus from 
Hormiscia by the presence of only two cilia on the zoospores 
in place of four. He has described the formation (fig. 3) 
Fic. 3.—Conjugation of microzoospores of Urospora penicilliformis x 1000 
(after Areschoug, |. c., tab. i, figs. 4-6). 
of the zygozoospore (first noticed by him in 1863) in U. 
penicilliformis in the following vivacious language :— 
**Microzoosporas celeriter natantes cum intuemur, duas 
' “Naturf. Gesellscb. in Ziirich,” Marz, 1870; ‘ Bot. Zeit.,’ 1871, pp. 
76, 89. For the development of the zoospores, cf. Braun, “ Rejuve- 
nescence in Nature,” ‘ Ray Soc.,’ pp. 148, 159. 
2 «Observationes Phycologice,’ Act. Reg. Soc. Sc., Ups., 1874. 
