254 



männlich und weiblich, vollends aber für den Begriff Hermaphrodi- 

 tismus." 



It is doubtless highly hazardous on the part of a zoologist to 

 venture an opinion that the botanists may, nay, must be, in error in 

 supposing spore-formation to be a later acquisition than sexual repro- 

 duction. 



We are bound to assume it to be a primitive process, which had 

 its origin in the necessity of reduction following a conjugation i). 



The primitive form of "sexual" reproduction or conjugation, — and 

 by either of these terms may be understood the 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 previous duplication of chromosomes. This very primitive 

 antithetic 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 modi- 

 fication, never towards its entire suppression. An attempt is made to 

 abolish one of its most obvious factors, spore-formation, in both In- 

 fusoria andMetazoa. 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 processes 



1) Another, and perhaps better, way of stating this would be that 

 an antithetic alternation of a very simple kind must be a consequence of 

 even the most primitive conjugation in plants also. That a suspicion of 

 an alternation of generations with spore-formation is more than justified 

 even in the simplest plants is proved by the facts of the conjugation of 

 Closterium, as described by Klebahn. 



After the conjugation of like gametes, the resulting zygote, i. e. its 

 duplicated nucleus, divides twice without resting-phase. Four nuclei 

 arise, two in each cell as there is only one fission of the protoplasm of 

 the zygote. As described by 0. Hebtwig ("Die Zelle und die Gewebe", 

 p. 224 — 225) "the two nuclei of each (of the cells) rapidly acquire a 

 difi'erent appearance ; the one becomes large and vesicular, whilst the other 

 remains small and later on disappears." This is strongly reminiscent of 

 the "pole nuclei" of the Infusorians ; indeed, these abortive nuclei must 

 be regarded as exactly the equivalents of the latter. The process is, 

 without question, a spore-formation with reduction. Of the spores formed 

 two are abortive. Thus here also the antithetic alternation would appear 

 to obtain. 



