MULTIPLICATION OF UN1CELLULARS 



33 



is, without complications, the fundamental fact in regard to 

 inheritance. 



It should also be borne in mind that many of the unicellular 

 organisms (Protozoa, at the base of the animal series ; Proto- 

 phyta, at the base of the plant series) are highly differentiated— 

 i.e. with great complexity of structure even within the narrow 

 limits of size (where a diameter of X \^W\ of an inch is considered 

 large) — and that many have very definite and interesting modes 





Gr 



Fig. 3. — Diagram of cell structure. (After Wilson.) 



PI. Plastids in cytoplasm or cell-substance ; cc. centrosome ; n. nucleolus ; Chr. chromo- 

 somes ; N. nucleus ; ct. general cytoplasm ; V. vacuole ; Gr. granules. 



of behaviour, such as swimming in a spiral, seeking light or 

 avoiding it, approaching certain substances and retreating from 

 others, trying one kind of behaviour after another, — functional 

 peculiarities — some of which cannot be described without using 

 psychical terms — which are also included in the inheritance. 



The case of a fragment of crystal growing into a complete 

 crystal is interesting enough, but that a fragment or spore of 

 apparent simplicity should reproduce the obvious complexity 

 of the unit from which it was separated is relatively more mar- 

 vellous. 



