THE 'NON-CELLULAR' TYPE 51 



simplicity, is furnished by the seaweed known 

 as Caulerpa Stahlii. As is shown by the 

 annexed illustration, the plant consists of 

 a creeping stem from which arise the erect 

 leafy expansions ; while the whole is anchored 

 by root-like structures which penetrate, or 

 adhere to, the substratum. In spite of this 

 high degree of external differentiation, there 

 is no internal partitioning, and no one of the 

 vast number of nucleated protoplasts, which 

 together make up the living substance, is 

 segregated physically from its neighbours by 

 obvious boundaries. But there is one signifi- 

 cant and interesting feature about the dis- 

 tribution of the nuclei in the protoplasm. 

 They are crowded at the growing points, 

 and are more widely spaced asunder in the 

 older regions. In this apparently trivial 

 circumstance we can discern exactly the 

 same arrangement as would have been ob- 

 served had the partitioning walls been actually 

 present, for the dividing cells in the growing 

 points always appear to be both numerous 

 and small, owing, of course, to the rapid 

 cell division which is going on in such regions. 

 Now this " non-cellular " or " syncytial " 

 (see p. 21) type of organisation entails 

 certain obvious disadvantages on its possessor, 

 but we find that in some instances the at- 

 tendant risks have been overcome in a 

 wonderful way. On coral reefs and similar 

 calcareous stations an alga known as Halimeda 

 Opuntia is sometimes found (Fig. 8). It resem- 



