12 THE FIRST PRINCIPLES OF HEREDITY 



This process of simple fission is the most common 

 method of propagation among the Protozoa and Proto- 

 phyta, but it can also be observed in species of higher 

 organization, even as high up as the worms. 



So we find among the Polypes some which multiply by 



division ; the newly - formed 

 individuals, however, do not 

 separate, but remain attached 

 to each other, thus forming 

 what is called a Polype - 

 stock. 



Among the worms, we have 

 the Bristle-footed worm 

 (ChcBtopoda) , which, either on 

 a shock or normally, breaks 

 up automatically into several 

 pieces. The sea- worm Myri- 

 anida forms, when dividing, a 

 whole chain of young worms. 

 In both these cases it is evi- 

 dent that after the division of 

 the mother-animal the com- 

 pletion of the daughter-worms 

 must take place by regenera- 

 ting the missing portion of the 

 body, either fore- or hind-end, 

 or both. Here, too, we can 

 still trace the close connection 

 between the process of reproduction on the one hand and 

 that of growth and regeneration on the other. 



Fig. 3. — Division of Amceba, 



[From Weismann, " The Evolu- 

 tion Theory.") 



A , before division ; B, the 

 nucleus divided ; C, the 

 daughter amcsbae. 



{b) Budding. 



While in division, as just described, the whole mother- 

 organism enters into the formation of the respective parts 

 of its progeny — the parent-animal thus being lost in, or 

 rather merged into, its own descendants — in budding the 



