36 GENERAL CONSIDERATIONS 



vidual of a syzygy forms a brood of gametes which copulate with 

 similar gametes from the other individual of the pair (see Turner, infra, 

 Chapter XII; and Kofoid, infra, Chapter XI). 



Coming at the end of a vegetative period during which single or 

 multiple divisions may have occurred, such gamete broods indicate a 

 change in organization which, if copulation does not occur, results in 

 death of the gametes. In other words gametes are so specialized that 

 they require a complemental combination to ensure normal metabolism 

 and life. In some gametes differentiation has been in the direction of 

 greater constructive activity, resulting in food-stored macrogametes 

 equivalent to egg cells; in others in the direction of greater katabolic 

 activity, resulting in a brood of microgametes equivalent to spermatozoa, 

 as in Coccidiomorpha. 



The happenings at conjugation need only be recapitulated, for the 

 phenomena are so well known that description here is unnecessary (see 

 Turner, infra, Chapter XII, for detailed accounts). In U role p/ us, shortly 

 after fusion of the anterior ends, the micronuclei of both individuals 

 begin a series of maturation divisions, and the third division gives rise 

 to the gametic nuclei. One of a pair of these remains in situ, while the 

 other, or migrating pronucleus, passes through the protoplasmic bridge, 

 unites and forms a fertilization nucleus by fusing with the quiescent 

 pronucleus of the other conjugant. Thus a mutual fertilization occurs, 

 the two migrating pronuclei in Uroleptus passing each other at the 

 apex of the united pair of cells (Fig. 13). After this is accomplished, 

 the two individuals separate, the amphinucleus of each conjugant di- 

 vides twice, and one of the products forms a new macronucleus, which, 

 after four or five days, is ready to divide. Another product forms a 

 new micronucleus. In the meantime the old macronucleus begins to 

 degenerate and is ultimately resorbed in the cytoplasm. The other 

 structures of the derived organization of the old organism are resorbed 

 and replaced by new ones. The young organism, with this new set 

 up, starts a new life cycle with an optimum of vitality (Fig. 14). 



Through these activities of conjugation, an old protoplasm with low 

 vitality is made over out of its own contained substances, into a new pro- 

 toplasm with high vitality. What explanation of this remarkable phenom- 

 enon can be given? The only apparent difference between the happen- 

 ings at division and at conjugation are: (1) fertilization, and (2) 



