322 Beard, Heredity and the epicycle of the germ-cells. 



In this way it conies to be a problem of embryology and deve- 

 lopment, and as such it falls within the province of the erubryologist. 

 This being- so, is it not remarkable, that the chain of germinal con- 

 tinuity should hitherto not have been completely grasped in any single 

 case? From my researches on the germ-cells 1 ) it is clear, that hitherto 

 no complete survey of the development from one generation to the 

 next has really been made. One phenomenon in the Metazoan life- 

 cycle has entirely eluded the observation of embryologists ; or, if they 

 have noted and recorded it, they have failed to realise its full signi- 

 ficance. This is the formation of the primary germ-cells with the 

 epoch, at which these appear upon the scene. 



Their very early origin before any trace of an embryo had 

 been laid down - - was long ago recorded in certain cases, among others 

 by Weismann, Biitschli, Grobben, Hitter, Metschnikoff and 

 0. Her twig. But these very instances only serve to strengthen my 

 contention; for in them the few primary germ-cells - from 2 to 8 in 

 number - were apparently so insignificant, that their formation at a 

 particular time seemed to be an incident of no moment; and its dis- 

 covery, like many other important finds, was passed over; because no 

 estimate could be set upon its value. 



Long ago Nussbaum concluded, that the germ-cells must diffe- 

 rentiate themselves at a very early period, before there was any trace 

 of histological differentiation in the embryonic foundation. But Weis- 

 maun 2 ), carrying with him practically all other zoologists 3 ), has deci- 

 dedly rejected this view; ,,because, as a matter of fact, the sexual 

 cells of all plants and those of most animals do not separate them- 

 selves from the beginning from the somatic cells". 



And this is just the question at issue. To allow the statement to 

 pass unchallenged might be taken as a tacit admission of its accuracy, 

 although every page of the present writing asserts its incorrectness. 

 The passage was written more than fifteen years ago, much has hap- 

 pened in the meantime, and it may no longer represent We ism a nil's 

 views. But the objection is recorded in the literature of embryology, 

 and it requires refutation. 



The argument contains two fallacies, and these rob it of all force. 

 Taking these in the order of their occurrence, the first is, that the 

 sexual cells of all plants do not separate themselves from the beginning 



1) J. Beard, The Morphological Continuity of the germ-cells in Eaja 

 batis. Anat. Anz. V. 18, p. 465485, 1900. 



2) A. Weismann, Die Kontimvitat cles Keimplasmas, Jena 1885, p. 44. 



3) Thus, for example, Oskar Her twig (Zeit- und Streitfragen der 

 Biologie, Heft I, p. 76, 1894). Here it is written n Zweitens gehb'ren die Ge- 

 schlechtszellen ebensogut zum Korper eines Organismus, von welchem sie sogar 

 oft den betriichtlichsten Teil, wie z. B. bei vielen Parasiten, ausmacheu, wie 

 jedes andere Gewebe etc." 



