RECENT ADVANCES IN 

 CYTOLOGY 



CHAPTER I 



CELL GENETICS 



The Cell and the Nucleus — Differentiation — Reproduction — Asexual and 

 Sexual — Haploid and Diploid Phases — Sexual Differentiation — Genotype and 

 Environment — Their Bearing on Chromosome Behaviour — And on Sexual 

 Differentiation. 



quippe, ubi non assent genitalia corpora cuique, 

 qui posset mater rebus consistere certa ? ^ 



Lucretius, De Rerum Natura, I, 167 — 168. 



I. THE NUCLEUS, THE CELL AND THE ORGANISM 



(i) The Problem. The object of the present work is to describe 

 the bodies responsible for heredity, to show how they live, move 

 and have their being. We now know that the Atomists were right ; 

 there are such bodies. But before considering them we must see 

 how organisms are constructed, how they reproduce and how 

 heredity expresses itself. Then we can examine the genitalia 

 corpora and better understand their relations with heredity. 



(ii) Structure. The living organism contains certain materials 

 which for various reasons are held to be non-living. Such, for 

 example, are the skeletal structures of plants and animals, consist- 

 ing largely of cellulose, calcium carbonate or chitin, their storage 

 products, such as starch, fats and glycogen, and their fluid contents, 

 such as cell sap and blood plasma. The rest of the plant or animal 

 body is described for convenience as the living substance or 

 protoplasm. Various non-living substances, such as water, can often 



^ For, if each organism had not its own begetting bodies, how could we 

 with certainty assign to each its mother ? 



R.A. CYTOLOGY. 1 1 



