CELLULAR STRUCTURE 35 



We see here a simple example of co-ordination 

 between the cells of an organism. It is true 

 that it is of a very rudimentary kind, but 

 the fact that an organism, originating in this 

 manner, possesses a definite form at all, is 

 a clear proof of its existence. 



The form of Apiocystis seems to be fairly 

 constant, but when conditions are suitable, 

 some or all of the protoplasts may escape 

 from the gelatinous sheath and swim away 

 as biciliate Chlamydomonas-like organisms, 

 though they are destitute, for a time at least, 

 of even a cell membrane. In this condition 

 they are known as Zoospores ; when one of 

 them settles down it becomes invested in a 

 cell wall secreted by the protoplasm, and 

 by repeated fission builds up another Apio- 

 cystis plant. This mode of reproduction by 

 means of zoospores is very common in the 

 algae, and it serves to recall the early stages 

 in the history of the race which is thus re- 

 peated during the beginning of the life of a 

 new individual. 



Now a pear-shaped organism is, by its 

 very form, rendered incapable of reaching 

 a large size, at any rate without such accessory 

 complications as are not to be thought of in 

 connection with primitive plants. There are 

 other lines of development which have proved 

 more fruitful from an evolutionary point 

 of view, and of these the flattened expansion 

 and the filamentous types represent the most 

 successful. Indeed, it is on these lines, or 



