PROTOZOA 



animal carriers such temperatures might prevail, e.g., on the moist 

 surfaces of insects during flight or in the bodies of warm-blooded 

 animals. The small amount of available nutrient under such con- 

 ditions might at the same time induce autogamy. Both of these 

 possibilities may be wide of the mark, but they and others need 

 to be looked into. The existence of regular karyotypic diversities 

 among local populations of inbreeders is a phenomenon that needs 

 to be accounted for. 



7. Conclusions and general comments. This survey of the 

 bearing of varietal characteristics on the breeding system is no 

 doubt incomplete. Increase of knowledge and further reflection 

 will probably bring to light the relevance of other characteristics. 

 Among those we have discussed, the period of immaturity stands 

 out as of major significance. The longer it lasts, the more oppor- 

 tunity close relatives have for dispersal before they can mate; 

 hence, the less likely that they will mate with each other. A very 

 long period of immaturity is thus an indicator of an outbreeder. 

 The absence of a period of immaturity marks an inbreeder. Being 

 ready at once to mate again, they are apt to mate with those 

 nearest at hand, i.e., their close relatives. 



The duration of the mating period is also of much importance. 

 This limits the period for finding a suitable mate. Probably no 

 great period of time is required to find a mate in the same local 

 population. In accordance with this, a short mature period marks 

 an inbreeder. If it fails to find a local mate in time, it undergoes 

 autogamy. Outbreeders need more time to find a suitable stranger 

 to mate with and they have long periods of maturity. Their chance 

 of success is enhanced, as in variety 16, by multiple mating types. 



Certain considerations apply to these two periods taken to- 

 gether. First, the available evidence indicates that migration from 

 one body of water to another is a relatively rare event; hence, 

 short combined periods of immaturity and maturity will as a rule 

 prevent breeding between different local populations and conjuga- 

 tion would occur between inhabitants of the same body of water. 

 The longer the duration of the two periods, the more time for 

 migration into or out of the local population and consequently 

 the more opportunity for outbreeding. Under the most favorable 



