PORIFERA, CCELENTERATA, VERTEBRATA 95^ 



into the endoderm. Something must be lacking in 

 the endoderm that is necessary to make a cell into a 

 germ-cell : that something is the germ-plasm." 



Several important contributions have appeared 

 within recent years which seem to deprive Weis- 

 mann's contentions of much of their importance. 

 For example, Goette (1907) has found that the germ 

 cells of many HYDROMEDUS^B may arise in the en- 

 toderm or in the ectoderm, and that in Clava multi- 

 cornis the germ cells are transformed half-entoderm 

 cells. After a long series of studies on ccelenterate 

 development C. W. Hargitt (1911) has attacked 

 Weismann's position in the following words : " That 

 there is any such region as may be designated a 

 'Keimzone' or ' Keimsta' tte ' may be at once dis- 

 missed as absolutely without warrant as a general 

 proposition. Furthermore, that the germ cells have 

 their origin in the ectoderm alone in hydromedusse 

 may be similarly denied and dismissed as unworthy 

 of further inquiry or doubt. And still further, I am 

 thoroughly convinced that the still more recent 

 controversy as to the hypothesis of the 'germ-plasm,' 

 if not as clearly a delusion as the preceding, is yet 

 without the slightest support from the ontogeny of 

 the group under review. 



"It is a matter of easy demonstration that in many 

 species of hydroids the egg may be followed in every 

 detail from its origin as an ectoderm or an entoderm 

 or interstitial cell through its gradual differentiation 

 and growth to maturation, as a distinct individual 

 cell, without the slightest tendency to multiplication." 



