48 GEORGE T. HARGITT 



sections made of the regenerative plasmodia. All the facts 

 point to the totipotency of the tissue cells under such stimulus. 



In some animals of different phyla reproductive organs are 

 present only during the breeding season, and at other periods no 

 germ cells can be recognized. In such cases the germ cells 

 must be differentiated from the tissues of the region which gives 

 rise to the reproductive organs. There is no evidence of a con- 

 tinuity of the germ plasm in these animals. In the vertebrates, 

 especially in mammals, recent observations point to the degen- 

 eration of all germ cells which are formed during foetal life; 

 the definitive germ cells are differentiated from the germinal 

 epithelium after birth. 



Pieces of tissue removed from the body will grow in culture 

 fluids, under certain conditions. In some cases the new growths 

 from this explanted tissue are embryonic in character, due to a 

 despecialization of the old differentiated tissues. Cancers, de- 

 veloped from tissues, are composed of cells more embryonic in 

 character than those from which they arose. These cells may 

 continue to live, grow, and divide indefinitely. Such observa- 

 tions indicate a less marked difference between body cells and 

 germ cells, and a greater plasticity and a more varied potency 

 in differentiated tissue cells, than has commonly been believed. 

 Such a weakening of the line of demarkation between these 

 two categories of cells tends also to weaken the germ-plasm 

 theory. 



So far as the coelenterates are concerned, the observations 

 upon the time and method of germ-cell origin; upon budding of 

 all types; upon regeneration of the usual sort, and regeneration 

 from Plasmodia formed by coalescence of isolated cells, all point 

 in one direction, viz., that there is no germ plasm in the sense 

 of Weismann. Furthermore, the origin of germ cells in some 

 phyla other than Coelenterata, the despecialization of differ- 

 entiated cells, and their behavior in tissue cultures and in normal 

 development, and the continued growth and division of body 

 cells in cancers, also present evidence contradicting the germ- 

 plasm theory. There are so many facts, from such different 

 sources and from so many phyla, which are inconsistent with 



