142 THE PROTOZOA 



it does not occur amongst organisms of the bacterial grade. Syn- 

 gamy is related to the life-cycle as a whole, and not specially to 

 cell-reproduction. In its effects on the cell-individual, syngamy 

 appears to have an invigorating effect, renewing vital powers that 

 have become effete and exhausted ; but in species that live in very 

 favourable conditions of nutrition, etc., whether such conditions 

 are due to artificial culture or to natural causes, such as parasitism, 

 syngamy may be deferred for a very long time, and may even be 

 completely in abeyance, or may degenerate into parthenogenesis 

 or autogamy. In its relation to the race, syngamy tends to level 

 down individual variations, and so produce true species amongst 

 the Protista. 



Before proceeding to discuss the nature and probable origin of 

 the syngamic process, it is necessary to take into account a process 

 which appears to be a universal concomitant of syngamy namely, 

 the process of nuclear reduction in the gametes. In all cases of 

 syngamy that have been carefully studied, it has been found that 

 the gametes differ from the ordinary cell-individuals of the species 

 in having undergone a process of so-called " maturation " which con- 

 sists essentially in nuclear reduction that is to say, in a diminution 

 of the normal quantity of the chromatin by so-called "reducing " 

 divisions of the nucleus. Hence the pronuclei which undergo 

 syngamic fusion differ in their constitution from the nuclei of cells 

 not destined for this process, and do not multiply, as a rule, under 

 normal conditions so long as they remain single. In some cases 

 among plants, however, the cells that have undergone nuclear 

 reduction may multiply by fission and produce a multicellular 

 organism (gametophyte) from which gametes ultimately arise ; in 

 this way is brought about the well-known alternation of genera- 

 tions of the ferns and flowering plants. Since, moreover, in Metazoa, 

 ova that have undergone nuclear reduction can be stimulated 

 artificially to start their development without fertilization, it is 

 clear that the nuclear reduction does not in itself inhibit further 

 development or cell-multiplication. 



True nuclear reduction in gametes must be distinguished clearly 

 from the process of elimination of effete or vegetative chromatin 

 which precedes the formation of the gametes or their nuclei, probably 

 in every case. As has been stated above (p. 72), vegetative and 

 generative chromatin may be combined in the same nucleus, or 

 may occur, the one in the form of a nucleus, the other in the form 

 of chromidia, or may constitute two distinct nuclei. When the 

 two are combined in one nucleus, a necessary preliminary to gamete- 

 formation is the purification of the generative chromatin of all 

 effete vegetative material. When the vegetative chromatin is 

 already separate from the generative, the latter alone takes a 



