45 2 Beard and Murray . — Reproduction in Animals 
phological mark would only be found in the maturation of 
the egg and in spermatogenesis. If the process were here 
a spore-formation, the whole Metazoan body, in which it took 
place, would represent the asexual generation, and any 
apparent alternation of generations in the life-cycle would be 
homologous 1 in character, not antithetic. But the total 
lack of homology between the organs of certain larvae and 
those of the adults which arise upon them, — as well as other 
facts and factors in course of publication elsewhere — leads to 
a suspicion that here we have a real antithetic alternation of 
generations masked by omission of the spore (apospory), and 
a consequent delay of the reducing division. Such a delay 
might easily arise as a result of the close association of the 
two generations observable in the development by substitution 
so characteristic of animals. In fact the frequency of substi- 
tution is one of the most striking differences between animal 
and plant development. 
As before stated, it is not intended in this place to attempt 
any proof that Metazoan development is a form of antithetic 
alternation of generations with apospory. That must be 
assumed, and the consideration of the evidences in favour of 
it be reserved for another place. 
On this supposition a comparison of Metaphytic and 
Metazoan modes of reproduction would be as shown in the 
table on the next page. 
It is thus apparent that the life-cycles of a higher Meta- 
phyte and of a Metazoan exhibit close correspondence, if 
animal development be a form of antithetic alternation of 
generations masked by aposporous formation of the sexual 
generation or gametozooid. The omission of a spore- 
formation has, as one of its results, the delaying of that 
reduction of the chromosome-number which must take place 
before the next conjugation. It thus happens that the cells 
of both generations contain a similar, i. e. duplicated, number 
1 As a matter of fact such a homologous alternation may become intercalated, 
and there is no intention of denying its existence alongside an antithetic one in 
many instances, such as Trematoda , Ascidia, &c. 
