16 GEORGE T. HARGITT 



entoderm, and the participation of all these layers in the for- 

 mation of the bud by evagination. He says, ". . . . conse- 

 quently I do not hesitate to proclaim the results of Lang as 

 erroneous, the conclusions drawn from them as utterly false." 



Downing ('05) believed sexual and asexual reproduction in 

 Hydra to be mutually exclusive, and implied a relation between 

 budding and germ cells. Montgomery ('06) supposed sexual 

 reproduction to be the more primitive, and asexual reproduction 

 to be a secondarily derived process; for him, regeneration and 

 asexual reproduction were dependent upon the presence of germ 

 cells. R. Hertwig ('06) found budding and sexual reproduction 

 proceeding side by side in Hydra and believed buds were produced 

 by the activity of the cells in all the layers. Mrazek ('07) and 

 Nussbaum ('07) confirm Hertwig on the simultaneous presence 

 of buds and sex organs in Hydra. The view of Hadzi ('09) was 

 in partial accord with Weismann and Lang, for he again renewed 

 the claim of the activity of only a certain layer to form buds in 

 Hydra. In his opinion the interstitial cells were the active 

 elements in producing buds, the other layers not participating in 

 any way. According to this view, the interstitial cells are a 

 source of all new growth, differentiation, and development in 

 Hydra, but they do not necessarily form a germinal tissue. 

 Tannreuther ('09) investigated budding still further, and for two 

 species of Hydra found, first, an increase in volume, and then a 

 proliferation of interstitial cells in the budding zone. There w^as 

 no migration of interstitial cells into the entoderm as Hadzi had 

 believed, for the layers remained distinct and unbroken through- 

 out the process. A distinct evagination occurs and cells of all 

 layers divide mitotically and are active in the budding process. 

 Furthermore, the division of cells of the ectoderm and entoderm 

 began about as soon as in the interstitial cells. Tannreuther's 

 work establishes the fact that budding in Hydra is an evagination 

 due to cell multiplication and growth, all layers in the budding 

 zone participating in the process. It seems probable that the 

 earlier division of the interstitial cells is merely an expression of 

 a more prompt response on the part of the indifferent cells than 

 of the specialized ectoderm and entoderm. I believe the fact is 



