82 Reproduction and Life-Cycles 



Among the Sarcodina, descriptions of syngamy have been published for 

 several Testacida (20-)) and Amoebida. Careful studies of chromosomal 

 behavior have not been reported. Some supposed instances of syngamy in 

 Amoebida have appeared in peculiar life-cycles which seem to be elim- 

 inated by the use of pure-line cultures (135) and the occurrence of sexual 

 phenomena in this order is still unproven. 



Although isogamy has been reported in some Sarcodina, gregarines and 

 Phytomonadida, certain of these examples involve gametes which are 

 similar in size and form but are distinguishable by vital staining or other 

 means. Miihl (183) noted that members of each pair, in syzygy of certain 

 gregarines, show different staining reactions with neutral red. These ob- 

 servations have since been confirmed and extended (138). Such differences 

 in staining reactions have been related to differences in oxidation-reduc- 

 tion potentials of the two gametocytes, which may differ also in the 

 quantity and distribution of cytoplasmic inclusions (138, 139). 



Physiological differentiation of similar gametes also has been reported 

 in Chlamydomonadidae. Species of Chlamydomonas may be homothallic 

 (synoecious) or heterothallic (heteroecious). In homothallic species a 

 single culture will develop gametes of both "sexes." Every motile flag- 

 ellate in such a culture is a potential gamete capable of uniting with a 

 flagellate of the opposite sex in the same culture. As observed in the 

 laboratory, syngamy occurs in heterothallic species only when two cultures 

 containing gametes of opposite sexes are mixed imder favorable condi- 

 tions. Moewus (180, 181, 182) has attributed such differentiation to 

 specific substances produced by CJilamydomonas.- The original assump- 

 tions were based upon certain effects produced by fluids from cultures. 

 (1) A motility factor in culture fluid stimulates rapid formation of flag- 

 ella upon addition to a culture containing palmella stages. (2) Termones 

 determine the sex of the gametes derived from palmella stages in hetero- 

 thallic races. Gynotermones cause production of female gametes; andro- 

 termones, the production of male gametes. (3) Gamones, concerned mainly 

 with mutual attraction of the gametes, modify sexually inactive flagel- 

 lates so that they can undergo syngamy. Androgamones from male cul- 

 tures cause agglutination of female gametes under favorable conditions; 

 gynogamones from female cultures have a comparable effect on male 

 gametes. 



Spectroscopic analysis of active substances, concentrated from large 

 volumes of culture filtrates, indicated that they were carotenoid deriva- 

 tives. In subsequent tests, the effects of culture filtrates were more or less 

 duplicated by certain derivatives of protocrocin. Accordingly, it was as- 

 sumed that protocrocin, synthesized by the flagellates, is broken down in 

 the presence of light in a series of reactions, each controlled by a par- 

 ticular gene. The products include picrocrocin, which in turn yields 



^ The work of Moewus and his colleagues has been reviewed by Sonneborn (220, 221). 



