RELATIONS OF OVA AND GEMM.E. 209 



The formation of ova has been here considered as in its 

 initial stage a modification of gemmation, in connection 

 with the maturation of the reproductive organs these 

 forming the parent stock, as it were, from which the gemmse 

 in question may he said to sprout. But, had we no ex- 

 amples of ova undergoing development in virtue of their 

 own plastic energy, we should miss in them one of the 

 most essential characters of gemmae. As the matter stands, 

 however, nature has provided us with a complete series of. 

 examples, establishing a well-marked transition from simple 

 gemmae, undergoing evolution in the ordinary way, to per- 

 fectly normal ova, absolutely dependent on fertilization by 

 the spermatic element. 



The view of the genetic cycle, which has been put forward, 

 is based on the existence of three successive stages in the 

 life-history of all organic beings, of which the first is pre- 

 liminary to the full development of the typical organization 

 of the species in the second, and the last has for its great 

 object the perpetuation of the race, by elaborating and 

 providing for the fecundation of ova endowed with a special 

 retentiveness of vitality and aptitude for development. In 

 one point of view, these three stages in the life of each in- 

 dividual may rather be regarded as a succession of so many 

 distinct individuals, each derived from the preceding by an 

 act of gemmation : using this word in its widest sense, to 

 imply simply the establishment of a new focus of construc- 

 tive and other vital action, in an extension of the substance 

 of the parent body. The new growth may be single or 

 multiple ; and it may separate from the parent as a 

 distinct organism, or it may in some way absorb it or take 

 its place. From variations in these points we may have 

 the alternation and multiplication of diverse forms, or we 

 may have merely successive phases of development in a 

 single individual. But, in all cases, the derivation of each 

 stage from the preceding may be held to be by some process 



