THE SPERMATOPHORE IN ARENICOLA 1039 
been in the same direction as in the higher plants. As pointed 
out by Coulter and Miss Pace, the end result attained in plants 
by the gradual reduction of the gametophyte generation to the 
point of complete extermination, in such forms as Pandanus, 
is entirely similar to the condition found in animals. Because 
the end results are similar is not prima facia evidence that the 
means of achievement in the course of evolution have been the 
same; it is very evident that in the higher plants such a condition 
as is found in Cypripedium, etc., is the result of a reduction of 
a gametophyte generation with the x number of chromosomes, 
for all steps in the process are evidently traceable. But nowhere 
in the animal kingdom, not even among the protozoa, is there 
any evidence of a corresponding gametozoic generation with a 
reduced number of chromosomes. 
REDUCTION AND TETRAD-FORMATION 
It is true that there is a striking similarity between the 
formation of the tetraspores in most plants and the development 
of the spermatids from the spermatocyte. It is rendered doubly 
suggestive by the fact that reduction occurs during both processes. 
Yet, even in the plants themselves, we are not warranted in con- 
cluding that all cells in which reduction occurs are homologous. 
Reduction occurs without tetraspore. formation in a sufficient 
number of cases, as in Lemanea, Chantransia, etc., to show that 
there is no fundamental phylogenetic association involved. The 
customary appearance of a fourfold division at time of reduction 
may be based on some fundamental! property of carbon compounds, 
possibly on the tetravalent condition of carbon itself; in which 
case it would not be strange to find tetrad formation common in 
plants and animals without assuming that, when occurring, a 
morphological homology is indicated. 
BEARD’S HYPOTHESIS 
In the preceding pages I have noted one hypothesis of the alter- 
nation of generations in animals—that proposed by Chamber- 
lain, and I have given my reasons for discarding it. Another 
