546 
Reginald Ruggles Gates 
Chaetopterus can be uiade to divide successively many times, without 
cleavage or the formation of separate uuclei. And zur Strassen 
(1898) found that the fusion of eggs of Ascaris may be brought about 
while the chromosomes maintain tbeir independence, as shown by the 
nuraber of chromosomes in the cleavage of such giant embryos. 
Wliile there is at present no direct evidence, this last alternative, 
namely, that the double number of chromosomes arose frorn 
a division of the chromosomes unaccompanied by nuclear 
or cell division, soon after fertilization seems perhaps 
the most likely. 
The more recent cytological investigations in plants liave revealed 
a number of genera in which some species liave approximately or 
exactlv double the number of chromosomes in closely related species. 
While the liistory of the forms having the doubled number of chro- 
mosomes is unknown, the Suggestion is obvious that some of them 
at least liave originated in a manner analogous to the origin of 0. 
gigas from 0. Lamarckiana. It is further of interest that in many 
cases the species having the higher numbers of chromosomes show 
some condition of apogamy or apospory. It would be of value to 
kuow whetlier the size relations of any of these species are the 
same as in the ease of gigas and Lamarckiana. A partial list of 
these species is given in Table V. 
It will be seen that in the genera Alchemilla, Antennaria and 
Hieracium, in the apogamous species the sporophyte number of chro- 
mosomes is about twice that in the normallv fertilized species. In 
Marsilia, however, this is not the case. In the Polypodiaceae (ferns) 
the chromosome counts show that the common number of chromo- 
somes is 64 (2 x), while in the apogamous species the numbers are 
invariably higher, although apparently not always double. The ad- 
mirable account of apogamy in Xephrodiwn Molle , by Yamaxouchi 
(1908) sliows that in the normal life cycle of this fern the sporophyte 
number of chromosomes is 128 or 132, but under certain conditions 
of the prothallia apogamy may be induced, in which case a sporo- 
phyte is produced directly by vegetative outgrowth from the gaineto- 
phyte, having 64 or 66 chromosomes. This is the reduced number 
for this species, but the 4 x number for many of the Polypodiaceae 
that are normallv fertilized [See Stevens (1898) and Gregory (1904)]. 
This makes it probable that a previous doubling had taken place in 
X. Molle , similar to the one which is known to liave occurred in the 
case of 0. gigas. This would explain why a sporophyte can now 
