254 



TIIALLOPHYTES. 



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 ccEnobium (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 (77) become free by the absorption of the gelatinous 

 envelope of the mother-family ; each daughter-family, again surrounded by a gelatinoug 

 envelope, grows to the original size of the mother-family. The sexual reproduction 



Fig. 167.— Development o{ PandortHa Morum (after Pringsheim) ; / a swarming family; //one 

 divided into sixteen daugliter-families ; /// a sexual family, the separate cells emerging from the 

 gelatinous envelope ; /y, V conjugation of the zoogonidia ; VI a zygospore just formed ; yil a 

 mature zygospore; VIII transformation of the contents of a zygospore into a large zoospore; 

 IXixee 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 (777) ; 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 (7^), but 

 gradually contracting into a ball (T); 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 



