SYNGAMY AND SEX IN THE PROTOZOA 139 



Tn Entamcefoa coli (Fig. 73) the process starts in like manner 

 from a uninucleate individual, the nucleus of which divides into 

 two, but the cell divides incompletely and only temporarily. Each 

 nucleus then breaks up completely into chromidia and disappears 

 from view. Some of the chromidia are absorbed, while from others 

 a secondary nucleus is formed on each side of the cell, so that two 

 nuclei reappear again in the cyst, but smaller than before and 

 staining feebly. Each secondary nucleus now divides twice to 

 form three nuclei on each side, two of which degenerate as re- 

 duction-nuclei, while the third in each caso persists as a gamete- 

 nucleus. As soon as the process of reduction is complete, the 

 incomplete separation of the two cells disappears, so that the two 

 gamete-nuclei lie in a single cell, which at this stage forms a tough 

 cyst. Now each gamete-nucleus divides into two pronuclei, those 

 of the same pair being slightly different from those of the other, 

 according to Schaudinn (133). Then a pronucleus of each pair fuses 

 with a pronucleus of the other pair, so that two synkarya result. 

 At a later stage each synkaryon divides twice, and eight amoebulae 

 are formed by division of the cell within the cyst. 



From these two examples, it is seen that autogamy is a process 

 of extreme inbreeding as regards the gametes. In typical cases 

 of syngamy the two gametes must be derived from two distinct 

 strains, and those of the same strain will not conjugate ; Schaudinn 

 (131), for example, observed that the gametes of PolystomeUa 

 crispa would only copulate when a couple came together in which 

 each gamete was of distinct parentage. In a great number of 

 Protozoa the differentiation of the gametes and their mode of 

 formation makes it certain that the couple which join in syngamy 

 are derived from different parents. On the other hand, in many 

 cases of autogamy that have been described, it is equally certain 

 that the conjugating gametes and pronuclei have a common 

 parentage, and it is hardly possible to consider autogamy otherwise 

 than as a degeneration of the sexual process, evolved in forms in 

 which one feature of true syngamy namely, the mixture of distinct 

 strains is, for some reason, no longer a necessity ; we shall return 

 to this point when discussing the nature and origin of the syngamic 

 process. It is possible, moreover, to recognize progressive stages 

 of the degeneration, as shown by .the two examples selected. In 

 the less advanced stage (Actinosph cerium) the parent cell divides 

 into two complete cells, each of which, after a process of matura- 

 tion, becomes a gamete. In the more advanced stage (Entamaeba 

 coli}, the division of the parent-cell is checked, and only its nucleus 

 divides, each daughter-nucleus becoming a pronucleus after reduction. 



The occurrence of autogamy has been asserted in a number of cases which 

 are, to say the least, extremely doubtful, as for example, the Myxosporidia 



