Jan. 1902.] BOTANICAL SOCIETY OF EDINBURGH 127 



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 or recorded it, 

 they have failed to realise its full significance. 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, Buetschli, Grobben, 

 Kitter, MetschnikofT, and 0. Hertwig. But these very 

 instances only serve to strengthen my contention ; for in 

 them the few primary germ-cells — from two to eight in 

 number — were apparently so insignificant that their forma- 

 tion at a particular time seemed to be an incident of no 

 moment ; and its discovery, 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 

 differentiate themselves at a very early period, before there 

 was any trace of histological differentiation in the embryonic 

 foundation. But AVeismann,^ carrying with him practically 

 all other zoologists,' has decidedly rejected this view ; 

 " because, as a matter of fact, the sexual cells of all plants 

 and those of most animals do not separate themselves from 

 the beginning from the somatic cells." 



And this is just the question at issue I 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 happened 

 in the meantime, and it may no longer represent Weis- 

 mann'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 



^ A. Weismann, " Die Continuitaet des Keimplasma's,'' Jena, 1885, 

 p. 44. 



-Thus, for example, Oscar Hertwig (" Zeit-und Streitfragen der 

 Biologic, Heft I.," p. 76, 1894). Here it is written, " Zweitens gehoeren 

 die Geschlechts/ellen ebenso gut zum Koerper eines Organismus, von 

 welcliem sie sogar oft den betraechtlichsten Theil, wie z. B, vielen 

 Parasiten, ausmachen, wie jedes andere Gewebe, etc." 



