GERM CELLS OF COELENTERATES 47 



become active, but there is no evidence that germ cells are 

 present. The budding phenomena of medusae resemble the 

 same processes in hydroids, since, in most cases, both body 

 layers evaginate to form the bud. In a few forms buds are pro- 

 duced from the gonads of the parent medusa, but even here this is 

 not a germinal process, for the buds are formed from all layers of 

 the animal; the germ cells of the gonad may participate in the 

 process, but only by behaving as tissue cells. A few medusae form 

 their buds from the ectoderm alone, and one investigator claims 

 that the bud originates from a group of oocytes, though he admits 

 this is a very unusual method, not applicable to most buds in 

 coelenterates. In no case are buds known to arise from a single 

 cell. While it may be possible, therefore, that budding is occa- 

 sionally a germinal process in medusae, this is rare; as an alter- 

 native explanation, other investigators believe both germ cells 

 and tissue cells are able to undergo regressive changes and 

 become embryonic. The embryonic cells have the ability to 

 form a new organism. The latter explanation would correlate 

 various types of reproduction, both sexual and asexual, in 

 coelenterates ; would correlate fission and budding in coelenterates 

 and other groups of animals, and would outline a possible evo- 

 lution of reproductive processes in coelenterates. The germ- 

 plasm theory, therefore, may be held not to apply to budding in 

 coelenterates, for it is contradictory to most of the facts of this 

 phenomenon. 



Regeneration is also held to be dependent upon the presence 

 of latent germ cells. There seems to be no direct evidence in 

 favor of this view, and the great body of facts concerning re- 

 generation in many phyla of animals contradict such an inter- 

 pretation. Especially do the observations upon regeneration 

 from isolated cells of hydroids disprove the germ-plasm theory. 

 When hydroid tissues are broken up into isolated cells the latter 

 undergo a despecialization and fuse to form syncytia. From 

 these masses complete and normal hydranths are regenerated. 

 When germ cells are present they are absorbed as food, and 

 take no part in the regenerative processes. The behavior of 

 the isolated cells has been followed with the microscope " and 



JOURNAL OF MORPHOLOGY. VOL. 33. NO. 1 



