804 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 
red spots and four cilia. Both red spots and cilia subse- 
quently disappear ; the zygozoospore passes into the resting 
condition, and eventually gives rise to a new Pandorina 
colony. The whole process of conjugation occupies at the 
most five minutes. 
With respect to other forms allied to Pandorina our know- 
ledge is far from complete. In Goniwm the formation of 
microzoospores is unknown. In Stephanosphera they have 
been described by Cohn and Wichura,! but their conjuga- 
tion has not hitherto been seen. In Hudorzna and Volvox, 
to which Volvocinacee is here restricted, the sexual process 
has attained a higher degree of differentiation and will be 
referred to further on. 
HypropicryeE®.—The well-known fresh-water alga Hy- 
drodictyon is in many respects nearly allied to the Pandorinee. 
The contents of the individual cells undergo separation into 
macrozoospores and microzoospores. Of the former from 
7000 to 20,000 are produced, of the latter from 30,000 to 
100,000. The swarming of the macrozoospores takes place 
entirely within the mother-cell, and the “net,” which is 
finally set free by its rupture, is the aggregate of these 
which has reached the resting condition. The microzoo- 
spores, on the other hand, are set free, and their ultimate 
destination is not properly known. Accor ding to Pringsheim* 
they are intended to reproduce the plant in a future season. 
It is highly probable, therefore, that they undergo a process 
of conjugation (although, as Sachs remarks, this has not 
yet been observed); and this may be the real meaning of 
the double spores which Cohn long ago figured,® but which 
he explained as the result of a casual adhesion or gluing 
together of two microzoospores adjacent to one another in 
the mother-cell. On this view the ‘ Doppelspore,’” which 
Cohn figures, would be the zygozoospore (fig. 1). 
oan 
Fig. 1.—Microzoospores (one with two 2 Bete doppelspore’ of Hydro- 
dictyon x 500 (after Gaba Ley). 
Cohn! also observed double spores in Cladophora (fig. 2), 
and Thuret in Hnteromorpha, in both of which genera, as 
See ‘ Quart. Journ. Mier. Sci.” 1858, p. 136, Pl. VI, figs. 26, 27. 
See Quart. Journ. Mic. Sci.’ n. s., vol. li, p. 54. 
“Untersuchungen tber die Entwickelungsgeschichte der mikrosko- 
pichen Algen und Pilze von Dr. F. Cohn.” ‘Nov. Act. Acad. Nat. Cur.,’ 
vol. xxiv (1854), pp. 225, 226. ‘Tab. 19, fig. 14. 
weo- 
