GERM CELLS OF COELENTERATES 21 



power to change or the stimulus to such change would be lacking. 

 Following this would come Bougainvillia niobe; the ability to 

 form buds is limited to a definite tissue, the ectoderm. Next are 

 those forms like Hybocodon in which all layers cooperate to form 

 buds, but this capacity for asexual reproduction is limited to a 

 definite locality in the parent. In this category one would place 

 most of the medusae which form buds, and all hydroids and Hydra. 

 Niobia dendrotentaculata represents a type in which the bud is 

 partly new growth and partly the already formed organs of the 

 parent; presumably all the regions of the body in such forms 

 would have the ability to undergo some transformation. This 

 type of budding would really be intermediate between regular 

 budding and fission. A final group would comprise medusae in 

 which a real fission occurs, and such a method of asexual repro- 

 duction is recorded by Mayer ('10, vol. 2, p. 280) for Gastroblasta 

 raffaelei Lang. A gradation such as this would correlate the 

 various kinds and degrees of asexual reproduction in Coelen- 

 terates with reproduction in protozoa, with regeneration, and 

 with sexual reproduction. It may even mark a possible evolution 

 of reproductive processes in Coelenterates, but would appear to 

 have no meaning according to the germ-plasm theory. 



c. Regeneration. Weismann ('93) takes the position that regen- 

 eration is due to the presence of germ plasm, since the latter is 

 the only substance capable of giving rise to all parts of the body. 

 As applied to plants, this involves the presence of germ plasm in 

 the cambium tissue wherever it is found. There is postulated 

 in plants an accessory germ plasm, concerned with the vegetative 

 development, and a primary germ plasm which is retained un- 

 changed till the germ cells are produced. But vegetatively 

 produced buds may later form reproductive organs and cells; 

 this requires the further assumption that accessory germ plasm 

 also contains primary germ plasm. This same involved and 

 intricate explanation is required to account for regeneration in 

 animals, if we believe that regeneration is due to latent germ cells. 



Morgan ('01) discusses a considerable number of theories of 

 regeneration and rejects the germ-plasm theory completely, 

 since he finds so many facts of regeneration utterly contradicting 



