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



So much so is this the case, that if both form embryos, these are like 

 twins. 



In the ancestry neither of the primary germ-cells ,A and A, had 

 ever been a Metazoon : neither they nor their ancestors had ever formed 

 parts of a Metazoan body. But their ancestry is continuous with a 

 long- line of germ-cells, and at regular intervals these were exactly 

 like certain sister-cells, which did develop and form embryos. Although 

 the cell A does not itself give rise to an embryo, it retains for itself 

 and for all its immediate progeny the properties of A, those characters 

 which, were it or its progeny to develop, would make it or them like- 

 twins with A. 



In the drama of heredity there are always understudies, which 

 for a certain essential period are endowed with all the identical pro- 

 perties of that germ- cell, from which the player arises. These under- 

 studies, the primary germ-cells, are never employed upon the stage as 

 such - - except in instances of like-twins but some of them, in new 

 guises and after new conjugations, are the immediate ancestors of 

 those, which become the acting characters in new scenes of the cyclical 

 drama of life. 



We now pass to the consideration of the primary germ-cells as 

 the equivalents of the spore-mother-cells of plants. The theory of an 

 antithetic alternation of generations as the basis of Metazoan deve- 

 lopment postulates something resembling the formation of spore-mother- 

 cells in plants. It is clear, that the final reduction of chromosomes 

 has been deferred to a later portion of the life-cycle in Metazoa as 

 compared with plants, and this fact was insisted upon some years ago 

 by J. A. Murray and myself 1 ). 



At that time we compared the two modes of development in tabular 

 form, and we postulated the formation of the embryo upon the asexual 

 generation or larva from a spore-mother-cell. Certain facts, supporting 

 this view, were cited, including E. B. Wilson's teloblasts of the 

 carthworn, which must be derivable from one cell. Finally, the spore- 

 mother-cells have appeared in the primary germ-cells of the present 

 research. 



In the above table ,,n" equals the number of chromosomes prior 

 to the duplication (,,2 n") at conjugation, that is, fertilisation. 



N. B. Although the primary germ- cells and the spores are shown 

 in the table in the same line, they are not equivalent. The former 

 correspond to the spore-mother-cells. 



In 1895 the writer was not sufficiently sanguine to believe it 



1) J. Beard and J.A.Murray. On the phenomena of reproduction in 

 animals and plants. Anat. Anz. V. 11, p. 234255, and also in Ann. of Bo- 

 tany V. 9, p. 441468, 1895. 



