26 THE FIRST PRINCIPLES OF HEREDITY 



produces in its turn, either by division (Aurelia) or by 

 budding (Hydrapolype), once more the sexual free-moving 

 generation. 



The interpolation of asexual reproduction by spores 

 between sexual generations is a well-studied phenomenon 



FIG. 19. ALTERNATION OF GENERATIONS IN THE COMMON JELLY- 

 FISH (AURELIA). (From Haeckel.) 



(From Geddes and Thomson, " The Evolution of Sex."} 



i, free-swimming embryo; 2, embryo settled down; 3 to 6, the 

 developing asexual stage ; 7 and 8, the formation of a pile of 

 individuals ; 9, their liberation ; 10 and 1 1, the free-living sexual 

 form. 



among lower plants. In the ordinary Fern we have the 

 big fern-leaf, the asexual plant, producing the familiar 

 spores at the back. These develop when in suitable ground 

 into an inconspicuous green organism, with male and female 

 sex-cells. From the union of both arises once more the 

 tall fern-plant. In the Moss we have a similar process, but 



