242 



fact, an application of his method to the other generation. Indeed, 

 it may be regarded as certain that what Weismann terms somatic cells 

 in both kingdoms owe their origin in all cases to sterilisation. 



"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 

 reduciog division of spore-formation, such a morphological 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 ^) 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 und 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 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 substitution is one of the most striking difference 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 consi- 

 deration 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 p. 243. 



It is thus apparent that the life-cycles of a higher Metaphyte 

 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 re- 

 duction 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 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 expla- 



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 etc. 



