576 THE LIFE CYCLE 



discovery by Jameson (1920) — later extended by Dobell (1925), Na- 

 ville (1931), Yarwood (1937), and Noble (1938) — that the matura- 

 tion division takes place in the first division of the zygote and that, aside 

 from the diploid zygote itself, the rest of the cycle is a haploid one. 



It is obvious that in the case of the male there is a fourth asexual 

 reproduction by multiple fission of a sixty-four-celled somatella, and 

 that this does not occur in the female. 



This life cycle is typical in having an alternation of sexual and asexual 

 reproduction upon which are superposed certain features, in part adap- 

 tive and in part more fundamentally a part of the cycle. The first of 

 these features is the building up of multicellular somatellas numbering 

 respectively four, two, ± sixty-four (x n), and + sixty-four in male 

 cells only, prior to multiple fission. The body thus formed is temporary, 

 lacking both nervous and hormonal mechanisms of integration to insure 

 the maintenance of interacting relations. The adaptive aspect lies in the 

 fact that these multiplicative reproductions make possible, with the least 

 expenditure of individuals, the quick utilization of the food supply in 

 the host's intestinal cells. 



This cycle from the cytological point of view, as well as the general 

 biological one, is atypical in the animal kingdom, though less so in the 

 plant kingdom, in that only the zygote is diploid and all of the rest of 

 the cycle is haploid. The fact that other Coccidiomorpha are known to 

 have the same limitation and that this subclass has affinities with the 

 flagellates, in some of which an odd number of chromosomes are known, 

 suggests that the primitive Protozoa are haploid and that the diploid 

 phase, like the polyploid, is a secondary evolutionary acquisition, de- 

 pendent, in part at least, on the union of individuals or gametes in 

 sexual reproduction. Thus both sex and sexual reproduction have had 

 their origin in the Protozoa. The limitation of the diploid phase to the 

 zygote only in Ehneria thus has a basic evolutionary significance. 



Another feature of this life cycle which also has a basic significance is 

 the fact that every one of the four phases of asexual reproduction results 

 in the formation of a somatella of from two to sixty-four cells, and that 

 the sexual phase also leads to a four-celled somatella. This evidence 

 clearly indicates that these Protozoa are as truly multicellular, as are the 

 early stages of the Metazoa. They undergo asexual reproduction as do 

 Metazoa, from Porifera to Quints, but with this difference: that the 



