CHAPTER IV 

 REPRODUCTION AND SEX 



It is difticult to find in the non-living world any analogue to the 

 multiplication of organisms. Even when a complex molecule gives 

 rise to two simpler ones, or a planet liberates a satellite, the resem- 

 blance to the division of an Amaba or to the budding of a yeast- 

 plant, is remote. The power of reproducing is one of the criteria 

 of Ufe. 



The general term reproduction includes the whole sequence of 

 processes by which new individuals arise. From a parent organism, 



Fig. 54. 



A Polychaet Worm [Myrianida fasciata). From Malaquin. The anterior body 

 (P) buds ofT from a posterior zone a chain of numerous individuals or 

 zooids (IND); E, eyes on the head of the original individual. 



or more usually from two parents, offspring take origin, often at 

 successive reproductive periods, which implies multiplication; these 

 offspring give rise in due time to others, and this implies a succession 

 of generations. It is not possible to separate reproduction in any 

 rigid way from growth, at the limit of which it usually occurs; or 

 from the activation of the reproductive organs at maturity, in which; 

 in Vertebrates, hormones are often concerned; or from the division 

 of labour implied in there being two sexes, egg-producing or female 

 individuals and s|x;rm-producing or male individuals; or from the 

 ways in which the s|xjrm-cell is brought into contact and union 

 with the egg-cell — a process in which the insemination, the polhna- 

 tion, and the like must be distinguished from fertilisation proper — 



