and Plants. Reducing Division in Metazoa. 453 
of chromosomes, and the reduction itself is necessarily deferred 
until the last possible moment, i. e. to the period of ripening 
of the sexual elements. ‘ Necessarily deferred ’ is undoubtedly 
the term to describe the fact, and the explanation of the why 
and wherefore of this affords an opportunity of considering 
a very obvious objection to the view here adopted. 
Metaphyte. 
Metazoan. 
zygote (an) 
Asexual generation 
sporophyte ( 2 n) 
spore-formation and re- 
ducing division. 
zygote (2n) 
larva (2n) 
I 
‘ Apospory ’ (reducing division 
delayed till last available mo- 
ment). 
adult form (2n) (gametozooid) 
I 
sexual organs (2n) 
reduction during oogenesis and 
spermatogenesis 
/ \ 
spermatozoon (in) egg (in) 
\ / 
zygote (2n) 
In the above table n equals the number of chromosomes prior to the duplication 
(2n) at conjugation. 
It may be urged that, if the fact of the occurrence of an 
antithetic alternation in animal development were admitted, , 
the reason for an aposporous formation of the gametozooid 
would not be at all obvious. Spore-formation with the 
necessary reduction might none the less occur at the proper 
juncture, and the gametozooid might, directly or indirectly, 
arise from one of these spores ; whilst the remainder, what- 
ever number of them there were, might be abortive. As 
a matter of fact, as will be presently demonstrated, something 
of this sort is the course of events in the conjugation of the 
Infusoria. It does not hold for Metazoa for the following 
reasons: — (1) Generally speaking, only one gametozooid 
makes its appearance on the larva, there are no traces of 
Sexual generation 
spores (in) 
gametophyte (in)'' 
sexual organs (in)' 
male female 
gamete (in) gamete (in) 
zygote (2n) 
