SYNGAMY AND SEX IN THE PROTOZOA 141 



and endure the vicissitudes of the outer world, until taken up by 

 a new host in which the parasite is set free from its cyst and starts 

 upon a fresh cycle of growth or multiplication without syngamy, 

 under the most favourable conditions of nutrition. 



2. As regards the effects of syngamy upon the species, it must 

 be pointed out, in the first place, that a great difference exists 

 between multicellular and unicellular organisms as regards the 

 effects of external conditions of life upon the sexual process. In 

 Metazoa the germ-cells, as already pointed out, are a race of cells 

 apart, and are sheltered by their position in the body from the 

 direct effects of external conditions at least, to a very large extent. 

 In Protozoa, on the other hand, there is no special race or strain 

 of germ-cells, but any individual may become a gamete or the 

 progenitor of gametes, and all alike are exposed to the direct 

 action of the environment. If, now, Protist organisms placed under 

 slightly different conditions of existence, tend to vary in their 

 characters as a direct consequence of environmental influences, 

 syngamy would check any such tendency, and would, on the con- 

 trary, tend to keep a given species constant and uniform in char- 

 acter, within narrow limits. Were there no intermingling of 

 distinct strains, such as syngamy brings about, individuals of a 

 species subject to different conditions of life would tend to give 

 rise to divergent strains and races ; syngamy levels up such diver- 

 gencies and keeps the tendency to variation within the specific 

 limits (compare Enriques, 112 and 113; Pearl, 124). If this sup- 

 position be correct, it would follow that no true species could exist 

 until syngamy had been evolved ; and if it be true that no syngamy 

 occurs in organisms of the bacterial type of organization, then such 

 organisms must be regarded as having diverged under direct 

 environmental influences into distinct races and strains, but not 

 as constituting true species. The " species " of bacteria would 

 then be comparable to the races of the domestic dog, rather than 

 to the natural species of the genus Canis. Not until syngamy 

 was acquired could true species exist amongst the Protista, a 

 condition which was probably first attained after the cellular grade 

 of organization had been evolved. 



The conclusions reached in the foregoing paragraphs may be 

 summed up briefly as follows : Syngamy is a process of inter- 

 mingling, in a single cell-individual, of chromatin derived from two 

 distinct individuals, gametes, which may exhibit differentiation 

 into " male " individuals, characterized by preponderance of 

 kinetic activity, and " female," in which trophic activities are 

 more pronounced. Syngamy is probably of universal occurrence 

 in organisms of the cellular type of organization, and from them 

 has been inherited by the higher plants and animals, but apparently 



