PANDORINA. 



729 



are observed to approach one another in pairs, as if seeking each other ; they come in 

 contact at their apices, and fuse into a zygote which is at first biscuit-shaped iJV) and 

 which gradually contracts into a sphere ( V), in which the two red corpuscles and the 

 four cilia at the enlarged hyaline spot are at first still perceptible, though they all 

 disappear soon afterwards. A few minutes after the beginning of the conjugation the 

 zygote is a spherical cell ( VI), which then remains dormant within its cell-wall for 

 a long time, its green colour passing over into a brick-red one. On placing the 



FIG. 411.— Development of Pandorina Moriim (after Pringsheim)- / a swarming family ; // a similar family divided into 

 sixteen daughter-families ; /// a sexual family, the individual cells of which are escaping from the gelatinous investment ; 

 IV, K conjugation of pairs of swarmers ; VI a zygote which has just been completed; /'// a fully grown zygote ; VI tl 

 transformation of the contents of a zygote into a large swann-cell ; l.\' the same after being set free ; .I'a young family 

 developed from the latter. 



dried up, and meanwhile considerably grown, spheres into water, germination begins 

 after about twenty-four hours. The external shell of the cell-wall breaks away, and 

 a layer within it swells up, and now contains one or two, or even three large swarm- 

 spores, which finally escape ( VIII and IX), and after swarming for a short time 

 surround themselves with a gelatinous envelope, and, by means of successive 

 divisions, break up into sixteen primordial cells, which now again form a fomily 

 as in Fig. /. 



Particular stress was formerly laid on the fact that both in Pandorina and in 

 the Conjugatae (e.g. Spirogyra), the two cells which unite sexually are equal in size 



