254 
THALLOPHFTES. 
In Pandorina Morum (Fig. 167) the complete course of development was followed 
by Pringsheim, this being the first instance that had been observed of the conjugation of 
zoogonidia. Pandorina is one of the commonest of the Pandorineae. The sixteen cells 
of a coenobium (Fig. 167, /) are closely crowded together, and surrounded by a thin 
gelatinous envelope out of which the long cilia protrude. The non-sexual multipli- 
cation results from each of the sixteen cells breaking up into sixteen smaller cells ; 
the sixteen daughter-families {II) become free by the absorption of the gelatinous 
envelope of the mother-family ; each daughter-family, again surrounded by a gelatinous; 
envelope, grows to the original size of the mother-family. The sexual reproduction 
Fig. 167.— Development of Pandorina Morin7i (after Pringsheim) ; / a swarming family ; // one 
divided into sixteen daugliter-families ; /// a sexual family, the separate cells emerging from the 
gelatinous envelope ; IV, V conjugation of the zoogonidia ; VI a zygospore just formed ; VII a 
mature zygospore ; VIII transformation of the contents of a zygospore into a large zoospore ; 
IX{xt& zoospore ; ^ young family produced from the last. 
is brought about in exactly the same way, but the gelatinous envelopes of the young 
families become softened, and the separate cells are thus freed and each swims about by 
itself (///) ; these free zoogonidia are of very variable size, rounded and green at the 
posterior end, pointed, hyaline, and furnished with a red corpuscle in front, where they 
bear the two cilia. Among the crowd of these zoogonidia may be seen some which 
approach in pairs as if they were seeking one another. When they meet, their points 
come in contact, and they coalesce into a body at first hour-glass-shaped (/^), but 
gradually contracting into a ball (F) ; in this ball the two corpuscles and the four 
cilia at the enlarged hyaline spot are still to be seen for a time; but these all soon 
