1038 , ELLIOT ROWLAND DOWNING 
ORIGINAL POSITION OF REDUCTION 
If reduction originally occurred in the primitive common ances- 
tor somewhere closely adjacent to the union of the gametes, the 
reduced number of chromosomes would exist for only a short 
period and might not occur at all. The major part of the life 
history of the forms would possess the somatic or diploid number. 
This is now the case for most animals and for many of the algae 
as already shown. In plants, then, the place of reduction in the 
life history has been shifted; the phenomenon has been postponed. 
In animals it occurs much nearer its original position. 
Reduction shifted 
Since in practically all animals and in many algae, the phenom- 
enon of reduction occurs before or during conjugation of the 
gametes, the preponderance of evidence appears in favor of such 
a position in the primitive common ancestors of plants and ani- 
mals. It is all the animals and many algae against the higher 
plants in favor of such an hypothesis. Text fig. 7, then, might 
nearly represent primitive conditions. Evidently following the 
gamete-bearing generation with its definite number of chromosomes 
would come a spore-bearing generation with the same number 
of chromosomes. This is true now in the Conjugales, Coleo- 
chaete, etc., and I believe in Volvocales and the animals. True, 
in Conjugales, Volvocales, etc., there are several spore-bearing 
generations following each other in succession. But if, for any 
reason, the alternation of generations be established by the omis- 
sion of all but one of these spore-bearing generations, there would 
be left the gametophyte and sporophyte generations as I conceive 
them to exist in Arenicola, only that the reduction has shifted 
from a position like that of fig. 7 of the text to a place before the 
conjugation of the gametes. For plants the shift in position has 
been, in the opposite direction—a shift that is seen progressing in 
text fig. 6 and completed in fig. 5. 
In Chamberlain’s theory of the alternation of generations in 
animals, he maintains that the shift in the animal group has 
