176 THE PROTOZOA 



So far only primary sexual differences that is to say, those 

 between the actual gametes have been discussed ; but, as has, been 

 stated above, the sexual differentiation may be thrown back, as it 

 were, into generations preceding the gametes. Thus, it is by no 

 means uncommon, especially in Coccidia and Haemosporidia, for 

 the gametocytes to be clearly distinguishable according to sex, the 

 female gametocyte having the cytoplasm loaded with reserve food- 

 material, and usually with a smaller nucleus, while the male gameto- 

 cyte has the cytoplasm clear and free from inclusions, and the 

 nucleus is relatively large. In Addea the male gametocyte is 

 very much smaller than the female (Fig. 154). In Cyclospora 

 carydytica, parasitic in the mole, the sexual differentiation is carried 

 back through generations antecedent to the gametocytes, and, 

 according to Schaudinn (147), male and female merozoites can be 

 distinguished. 



The various types of polymorphism that have been discussed in 

 this chapter may be classified as follows : 



1. Adaptive polymorphism. 



(1) Passive. 



(2) Active. 



2. Ontogenetic polymorphism. 



(1) In size alono. 



(2) In structure also. 



(a) Recapitulative. 



(b) Adaptive. 



3. Sexual polymorphism. 



(1) Primary (of gametes). 



(2) Secondary. 



(a) Of gametocytes alone. 

 (6) Of other generations also. 



In the task of unravelling the complicated life-cycles of Protozoa, 

 it is of the, greatest importance to distinguish clearly the significance 

 of the various forms that are seen, and there can be no doubt that 

 failure to do so has often been a source of error. With some writers 

 it is an obsession to ascribe all differences to sex, and to interpret, 

 for instance, in the development of trypanosomes, all bulky forms 

 as females, and all slender, active forms as males, quite regardless 

 of the behaviour of the forms thus designated. It is far more 

 probable that in the majority, at least, of such cases the bulky 

 forms are related to the multiplicative, the slender, active forms to 

 the propagative function, respectively, and that the differences 

 between them have no relation whatever to sexual functions, either 

 in the forms themselves or in their descendants. 



