BIOLOGY IN ITS WIDER ASPECTS 1229 



THE CELL-CYCLE 



Continuing our descending analysis, from vegetative and repro- 

 ductive systems and organs, through tissues to their cellular life, 

 we cannot but regret that the fruitful and intensive microscopic 

 observations of wellnigh three generations since Schleiden, Schwann, 

 and other contributors to the establishment of the cell-theory — and 

 despite the physiological and pathological insight of Goodsir, 

 Virchow, and others — have as yet remained too simply morpholo- 

 gical; though in that respect of ever increasing interest — witness 

 our new intensive knowledge of cell-structure and division, and 

 even of nuclear chromosomes and genes as well. Yet with all the 

 interest of these phenomena, as even of the genes for heredity, we 

 still lack explanation of their working; in short, we have still too 

 little of physiological interpretation. Hence we cannot but plead 

 for more consideration of the simple doctrine which underlies not 

 only our "Evolution of Sex", "Sex", and "Evolution", but is in- 

 creasingly a general conception for evolution — that of the cell not 

 simply as subject for structural analysis, but as more or less pre- 

 senting, as a whole, and in its development and changes, physio- 

 logical, and thus morphological, a cell-cycle. That is, a potentiality 

 and frequent manifestation of cyclic changes, of functioning and 

 form accordingly; and these intelligible in physiological terms, as 

 associated with its varying metabolism. For when the constructive 

 and anabolic side of this ultimate and dual chemical and physical 

 life-process of all living bodies, small or great, simple or compound, 

 predominates, we have growth, with relative passivity, and tendency 

 to spheric form. Whereas, when destructive and katabolic activities 

 predominate, there must be reduction in bulk from wear and waste, 

 yet with liberation of kinetic energies, even to movements, and 

 these at very various levels of intensity, as from simplest Amoeba to 

 most active infusorian or monad. On the reproductive side too, the 

 contrast is carried to its extreme, in the passive and often large 

 and well-stored ovum, and the minute, but long sustainedly active, 

 spermatozoon. The main forms of Protozoa, and even of Proto- 

 phytes, thus also range from encysted and long enduring passivity 

 to moderate or intense mobility on emergence, witness the startled 

 surprise of the first discoverer of this striking phenomenon, recorded 

 in the title of his paper, The Plant in the Moment of Becoming an 

 Animal. 



This alternation of growth to maximum, followed by a period of 

 rest, yet renewing to activity, is widely characteristic; first of the 

 Protozoa in their development, so that even the apparently life- 

 long encyst ment and passivity of the parasitic Gregarines is pre- 

 ceded by a brief yet distinct motile phase, while conversely the 



