THE SPERMATOPHORE IN ARENICOLA 1037 
THE GAMETOZOON, A 2X FORM 
Botanists, reasoning on the basis of the fact that the disappear- 
ing gametophyte in the higher forms possesses the haploid num- 
ber of chromosomes, have been led to assume, not only that the 
gametophyte represents a reversion to the primitive type, but 
also that this primitive plant possessed the « number of chro- 
mosomes. Reasoning in an analogous manner, we should be 
forced to assume, that, since the gametozoon possesses for most 
of its life history, the 22 number of chromosomes, so the prim- 
itive animal type did not have the reduced number. This dis- 
tinction between plants and animals has long been recognized. 
“So far as groups of plants above the thallophytes are concerned, 
the period of chromosome reduction has been found to be always 
associated with sporogenesis and never with gametogenesis as 
in the case of animals.’”’ (Yamanouchi; Polysiphonia, p. 43.) 
The difference may help to trace the gradual separation of the 
plant and animal types in the course of evolution. Upon this 
distinction, for instance, Dobell rests his belief in the plant affin- 
ities of the Phytomonadina (The structure and life-history of 
Copromonas subtilis, p. 112). The discovery already mentioned 
that Volvox has reduction occurring during gametogenesis would 
justify, in a measure, the classification of the form as an animal 
rather than as a plant. 
THE COMMON PROTOTYPE 
Presumably plants and animals have come from a common an- 
cestor. Now in all higher animals reduction occurs near the 
close of the gametozooic generation. It occurs, in all higher 
plants, near the close of the sporophyte generation. In the com- 
mon ancestor it must have occurred at a point between these 
two extremes, possibly during or in close connection with the con- 
jugation of the gametes. Such a possibility is rendered probable 
from the fact that, in thallophytes and protozoa, the reduction 
occurs at variable times in the life histories, usually as an adjunct 
of the union of the gametes, as if that variation were dominant 
which later becomes fixed in the two prevailing plant and animal 
types. 
