and Plants . Reducing Division in Metazoa . 451 
Notwithstanding all those facts of Protozoan modes 1 of 
reproduction which may appear to tell against this, notwith- 
standing all the botanists believe about the secondary nature 
of alternation of generations, it must be insisted that a simple 
antithetic alternation of generations was obligatory from the 
very nature of the original conjugation. 
All subsequent higher developments must be considered as 
effected by further specializations on the original ‘ plan.’ 
The Protozoan stage might be improved upon by the one 
generation or the other, or by both. The conjugating 
generation may have become Metazoan, or the spore- 
producing one, or both together may have undergone the 
higher evolution 2 . It is probable that there were originally 
variations here, and some of these still persist. In plants the 
amplification of the zygote stage has given rise to the sporo- 
phyte, which is sharply separated from the sexual generation 
or gametophyte by a one-celled stage (the spore) and a re- 
ducing division. The whole of the cells of the gametophyte 
must be looked upon as morphologically aequivalent, some 
becoming differentiated as vegetative organs by sterility, 
others retaining the primitive character of becoming con- 
jugating gametes. Bower 3 has attempted with some success 
to derive the members of the sporophyte by a similar steril- 
ization of sporogenous tissue. The standpoint here taken up 
is, in fact, an application of his method to the other genera- 
tion. Indeed, it may be regarded as certain that what 
Weismann terms somatic cells in both kingdoms owe their 
origin in all cases to sterilization. 
When one seeks in the higher animals for an equivalent of 
the alternation of generations in plants in the light of recent 
work on the reducing division of spore-formation, such a mor- 
1 In the sequel an attempt will be made to show, by concrete instances which 
have been thoroughly investigated by other observers, that many of these are 
secondary in nature. 
2 This must be held as true for the plant kingdom also. 
3 Bower, F. O., Studies in the Morphology of Spore-producing Members. Phil. 
Trans. 1894, B. 
