374 INTRODUCTION TO CYTOLOGY 



organisms there is no discernible structural difference between the 

 male and female gametes, and further because structural differences 

 may be annulled in certain instances (some gregarines). Any material 

 differences present in visibly similar gametes are more probably chemical 

 in nature, the structural difference being of a molecular order. Indeed, 

 there is probably no physiological difference without a structural differ- 

 ence of this sort. If the term structure be extended to include molecular 

 constitution the discussion over the relative priority of structural and 

 physiological differentiation becomes futile, for at this level the two are 

 aspects of one and the same change. It is only when we restrict the term 

 structure to the grosser, visible features that we can speak of physiological 

 differentiation as preceding alteration in structure. Ultimately structural 

 and functional changes are indistinguishable. Just as in the gametes 

 of the two sexes, so also in the unisexual individuals which the gametes 

 produce there may be striking differences of both morphological and 

 physiological natures; but if we use the term morphological only with 

 reference to visible features the primary distinction between the sexes 

 in organisms of all grades is apparently one of physiological state, this 

 distinction and its result (sexual reproduction) being of the greatest 

 biological importance. 



Taking into consideration all organisms, low and high, it seems 

 probable that any dimorphism among the gametes of one sex or the other 

 has in some way been developed in connection with the maintenance of 

 the above mentioned difference in physiological state in organisms of a 

 certain level of advancement. Different organisms show all degrees in 

 the differentiation among the gametes of one sex: some are marked by an 

 absence of any visible difference either in the gametes or in the her- 

 maphroditic individuals produced; in others the gametes (of one sex) are 

 visibly similar but result in male and female individuals in regular ratio; 

 and finally there are those in which the gametes are of two kinds both 

 physiologically and morphologically, the two kinds controlling the pro- 

 duction of individuals of the two sexes. It is in organisms of the last type 

 especially that the question of sex-determination finds the adherents of 

 the chromosome-Mendelian theory and those of the metabolic theory 

 in disagreement. Is the sex of the individual inevitably dependent 

 upon the type of gamete functioning (usually the kind of sperm fer- 

 tilizing the egg), or is it possible to overcome the effect which the 

 chromosome mechanism may have by influencing sufficiently the 

 metabolism of the organism? If the sex of an individual is so changed, 

 does the chromosome mechanism undergo a corresponding alteration? 



Those who have developed the chromosome-Mendelian theory have 

 perhaps too often held that the two sexual states, maleness and female- 

 ness, are in their ultimate analysis mutually exclusive that they are two 

 fundamental and qualitatively different alternative characters depending 



