680 JOHN BEARD, 



latter group, published in 1883 under the title "Die Entstehung der 

 Sexualzellen bei den Hydromedusen", that the doctrine of the origin 

 of germ-cells from somatic cells has become so firmly engrafted on 

 the science. 



In the interval from 1883 lie many of Weismann's own classic 

 memoirs, which, perhaps more than the writings of any other observer, 

 cast grave doubts on the validity of certain of his conclusions in the 

 aforesaid work. 



It is not my intention to examine, or to attempt the task of 

 criticising this great research — to do so except on the basis of new 

 observations would savour of presumption — but, regarding it in the 

 light of my own work, certain points in it call for notice. 



As in 1883, so also in 1893 in his "Germ-plasm" Weismann sees 

 no objection to the thesis, that even for a prolonged period the 

 "Keimbahn" or germinal track may be in the somatic cells. The 

 theory, for it is not an estabUshed fact, needs two hypotheses in its 

 support, a continuity of a hypothetical substance, the germplasm, and 

 its presence in all sorts of somatic cells, which, according to him, 

 may become germ-cells. Both of these hypotheses become unnecessary 

 on the demonstration of a morphological continuity of germ-cells, as 

 shown in the closing pages of the present writing. 



His hydroid work might be described, not as showing the origin 

 of germ-cells at all, but as revealing and following their wander- 

 ings. In the light of my work on the skate he shows no origin of 

 germ-cells ; for he only treats of colonies of polypes, and does not 

 go back to the youngest stages or phases, except of buds on the stem ! 



That certain germ-cells are in the manubrium or elsewhere as 

 regular members of an epithelium proves nothing, for the same sort 

 of thing obtains in the skate and other vertebrates after a certain 

 portion of the development is completed, and in the skate 

 the germ-cell has only taken up its position as a member of the 

 epithelium after its wanderings are over. 



No real transitions from epithelial or ectodermal cells to germ- 

 cells are depicted. Certain of the figures are supposed to reveal this 

 passage, but only in semi-diagrammatic ftishion and the magnification 

 employed is far too low, the highest being 480. 



As a history of the wanderings of the germ-cells the facts he 

 describes are of extreme interest and importance, regarded as show- 

 ing the various origins of germ-cells — for, if Weismann's conclusions 

 be valid, their name is legion — they are incomprehensible and in- 



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