467 
The Conjugation of the Infusoria. 
union of at first like zygotes, and afterwards of unlike but 
none the less morphologically equivalent ones — apart from 
fission, was from its very nature bound up with an asexual 
process, or spore-formation, leading to reduction of the pre- 
vious duplication of chromosomes. This very primitive anti- 
thetic alternation of generations still exists, and is bound to 
remain in a more or less modified form in both animals and 
plants, in consequence of the duplication which results from 
any conjugation. The tendency in higher forms has been in 
the direction of its modification, never towards its entire 
suppression. An attempt is made to abolish one of its most 
obvious factors, spore-formation, in both Infusoria and 
Metazoa. In the former this results in the formation of 
functionless vestigeal spores, but the fact of a spore-formation 
is very evident, for these are here necessary factors in the 
evolution of conjugating gametes. 
In Metazoa it has been avoided by apospory. The pro- 
cesses differ considerably in the two cases, because the lines 
of evolution have been so divergent. But, although the 
means adopted to attain the end (i.e. reduction of the dupli- 
cated number of chromosomes), is not by any means identical 
in both, the result is the same, the attainment of cells (nuclei), 
in which the primitive or reduced number of chromosomes 
is present. In the one case the reduction is associated with 
the formation of abortive spores (pole-nuclei), in the other 
with abortive eggs, i.e. abortive gametes (polar bodies). 
Even in the steps leading to the spore-formation abortive 
products may be formed, as in Onychodromus grandis, where, 
in addition to abortive spores, functionless, and therefore 
abortive, spore-daughter-nuclei obtain (woodcut 12 b). 
The same form is also interesting as presenting at the close 
of the division D a number of abortive gametes, which are to 
be regarded as in a certain sense the homologues of the 
‘ polar bodies ’ of Metazoan oogenesis. Similar abortive 
gametes are also present at the corresponding stage in 
Vorticella. 
Boveri has shown that the ‘ polar bodies * of Metazoa 
