CHAPTER XVIII 



THE DETERMINATION OF SEX 



The association of chromosomes with sex has already been 

 mentioned in Chapter XVI. For many years their behaviour has 

 been regarded by many scientists as an adequate explanation of 

 sex determination, although anomalies of various kinds have 

 required ingenious explanations to harmonize them with the facts 

 of chromosome behaviour. 



At present the state of experimental work in this field enables 

 us to say that the chromosomes are definitely associated with 

 sex determination under ordinary conditions and that sex is there- 

 fore inherited in many cases as a Mendelian character; we now 

 know, however, that this is only a part of the story and that 

 other factors, possibly many others, are concerned with sex deter- 

 mination. These other factors have been discovered in some 

 cases and placed under control with such accuracy that the sex 

 of an individual, not merely superficial but also fundamental 

 characters, has been determined independently of its chromosomal 

 complex. 



What Is Sex? Among the fundamental principles of biology 

 reproduction is recognized as a primary characteristic of living 

 matter. In the simplest unit, the cell, reproduction is a common 

 function and in complex organisms every individual plays some 

 direct part in the production of new individuals unless it is special- 

 ized for other purposes in a colony of different kinds of individuals. 



In its simplest form, the process is one of subdivision into two 

 new individuals as nearly as possible like each other and like 

 their common parent. This process of subdivision is carried to a 

 point where only a small portion of the parent buds off to form a 

 new individual ; the parent does not lose its identity in the process, 

 but may continue its normal vital processes even while it gives 

 rise to a new generation. It is only a step from this process of 

 budding to the development of specific reproductive cells or 

 spores, each of which after separating from the parent is potentially 

 a new organism. Between this and sexual reproduction there is 



325 



