GENESIS. 277 



Distoma-l'dTvas with which it becomes filled. Speak- 



ing generally, the degree of disintegration becomes less 

 marked as we approach the higher organic forms. Plants of 

 superior types throw off from themselves, whether by gamo- 

 genesis or agamogenesis, parts that are relatively small; 

 and among superior animals there is no case in which the 

 parent individuality is habitually lost in the production of 

 new individuals. To the last, however, there is of 



necessity a greater or less disintegration. The seeds and 

 pollen-grains of a flowering plant are disintegrated portions 

 of tissue; as are also the ova and spermatozoa of animals. 

 And whether the fertilized germs carry away from their 

 parents small or large quantities of nutriment, these quanti- 

 ties in all cases involve further negative or positive disinte- 

 grations of the parents. 



Except in spore-producing plants, new individuals which 

 result from agamogenesis usually do not separate from the 

 parent-individuals until they have undergone considerable 

 development, if not complete development. The agamo- 

 genetic offspring of those lowest organisms which develop 

 centrally, do not, of course, pass beyond central structure; 

 but the agamogenetic offspring of organisms which develop 

 axially, commonly assume an axial structure before they be- 

 come independent. The vegetal kingdom shows us this in 

 the advanced organization of detached bulbils, and of buds 

 that root themselves before separating. Of animals, the 

 Hydrozoa, the Trematoda, and the Salpce, present us with 

 different kinds of agamogenesis, in all of which the new 

 individuals are organized to a considerable extent before 

 being cast off. This rule is not without exceptions, however. 

 The statoblasts of the Plumatella (which play the part of 

 winter eggs), developed in an unspecialized part of the body, 

 furnish a case of metagenesis in which centres of develop- 

 ment, instead of axes, are detached; and in the above-de- 

 scribed parthenogenesis of moths and bees, such centres are 



detached from an ovarium. 

 19 



