SUMMARY OF CONCLUSIONS. 219 



Pulliilation of similar derivative structures to a 



variable extent. 

 Gemmation ultimately of the proper reproductive 



organs — sperm sacs and germ sacs — containing 



their characteristic corpuscules, for the purpose of 



fecundation. 



§ 5, This formula, and that at p. 216, as constructed to 

 include the different forms of alternation of generations 

 above referred to, of course has not, in general, all its 

 details obviously represented in any one species. The 

 alternation comes out prominently in one stage, wliile the 

 con-esponding changes are more or less suppressed or cur- 

 tailed in the others. It is, perhaps, of most frequent 

 occurrence in the gamomorphic stage, next in the proto- 

 morphic, and least so in the orthomorphic ; while there 

 appear to be but few cases, as already mentioned, in which 

 it is distinctly met with in all the three stages. 



In one of the tables given in the Appendix, the orders 

 best known, for examples of this kind, are arranged under 

 the heads of the life periods in which the more obvious- 

 phenomena of alternation occur. In those that follow, an 

 attempt has been made to arrange, under the same heads, 

 some of the most striking phenomena in the genetic cycle, 

 both of alternating and non-alternating species of plants 

 and animals. 



It may be mentioned, in conclusion, that however great 



the effect of these processes of gemmation and puUulation 



may be in modifying the external form of those species 



in wliich they prevail extensively, little or no relation ca,n 



be traced between the peculiarities of the genetic cycle and 



the affinities of the species, as recognized by systematic 



naturalists. We have seen that totally different laws of 



gemmation prevail in nearly allied orders, as in Cestoid and 



Trematode worms among animals, and in mosses and ferns 



L 2 



