283 



THE CELL 



Fig. 157. Development of Pandorina morum (after Pringsheim ; from Sachs, Fig. 411) : 

 / a swarming family; If a similar family, divided into sixteen daughter-families; III a 

 sexual family, the individual cells of which are escaping the gelatinous investment; IV, 

 V conjugation of pairs of swarmers; VI a zygote, which has just been completed ; VII 

 a fully grown zygote; VIII transformation of the contents of a zygote into a large swarm- 

 cell ; IX the same after being set free ; X a young family developed from the latter. 



swim about independently (Fig. 157 III, IV). These swarm- 

 cells, which are oval, and (with the exception of the anterior, 

 somewhat pointed, hyaline end) are green in colour, possess a red 

 pigment spot and two flagella ; they are somewhat unequal in 

 size. However, in this respect a marked sexual differentiation 

 is not apparent in Pandorina. For when swarm-cells from two 

 different colonies approach each other, it is seen amongst the 

 crowd that sometimes two small ones, sometimes two large ones, 

 and sometimes one large and one small unite together (Fig. 157 

 IV, V). 



