276 THE AMEBIC AN NATURALIST [Vol.LII 



process of fundamental evolutionary significance oc- 

 curred, unless it be the various mechanisms devised to 

 promote or to insure cross-fertilization, and which may be 

 interpreted as variations tending to perfect sexuality. 



Coincident with the general trend of plant evolution 

 just mentioned, two important changes in the nature of 

 retrogressions occurred, which have persisted in many 

 species. A new type of asexual propagation arose, 

 apogamy, which though it appeared under several guises, 

 apogamy in the narrow sense, parthenogenesis and poly- 

 embryony, is none the less asexual reproduction returned 

 under another name and apparently with no particular 

 advantages over the older types. Further, hermaphrodit- 

 ism was developed and has persisted in numerous lines. 

 We may be wrong in calling hermaphroditism a retro- 

 gression, for it has the great advantage of a certain 

 economy of effort in the production of gametes, but never- 

 theless it is certainly a change which per se is in the 

 opposite direction from that established when sex was 

 first evolved. A moment of consideration not only makes 

 this clear, but gives us a pretty satisfactory proof that 

 the gain made when continuous multiplication was halted 

 for a time by the intervention of a fusion at the genesis 

 of sexual reproduction was in some way connected with 

 the mixture of dissimilar germplasms. This conclusion 

 is hardly avoidable from the fact that although herma- 

 phroditism retained the cell fusion mechanism of gono- 

 chorism it was still necessary for Nature to evolve means 

 for cross-fertilization. And the multitude of ways in 

 which she solved this problem must mean that an im- 

 mense advantage was secured. 



In spite of the great morphological differences between 

 animals and plants, the essential evolutionary changes 

 affecting reproduction in the two kingdoms have been 

 so similar as to be almost uncanny. Accepting the divi- 

 sion of animals into twelve phyla as recognized by many 

 modern zoologists (Parker and Haswell), one finds the 

 following facts regarding reproduction. Asexual repro- 



