Beard, Heredity and the epicycle of the germ-cells. 305 



penecl, that so great an investigator and thinker as Darwin could 

 set up his provisional hypothesis of pangenesis. 



When in one of the higher animals, the skate, the formation of a 

 whole battalion of germ-cells is found to take place prior to the ap- 

 pearance of any trace of the embryo, a change comes over the scene: 

 the apparent law and its exceptions exchange positions, with the con- 

 sequent disappearance of the former. 



In the life-cycle of the skate (including in this all that happens 

 from the union of egg and sperm, until new eggs and sperms are 

 formed) the origin of the germ-cells fills in so large a space as to 

 overshadow completely everything else. For this reason the formation 

 of an embryo may be described as a mere incident in the life-cycle. 



Two primary germ-cells and five hundred and twelve are very 

 different numbers. If the full significance of this should not be ap- 

 parent, a glance at the diagrammatic representation of the life- cycle 

 of the skate may serve to make it so. The diagram is, however, in- 

 correct! In the portion showing the origin of the primary germ-cells 

 these have only been drawn to six divisions, giving 64. To exactly 

 embrace the full significance of the discovery the drawing ought to 

 include three further divisions, yielding 512 germ-cells at P. G. C. 



That is to say, to accurately represent the conditions in embryo 

 no. 454, for example, the diagram ought to be at P. G. C. eight 

 times as wide as it is at present! 



When I see in this diagram some of the results of twelve years 

 of work, the reader will, perhaps, pardon me, if I linger to say 

 something more concerning it and its origin. Some parts of it will be 

 familiar to every embryologist, thanks to the work of Boveri, 

 0. Her twig, and others: the other and unfamiliar portions are 

 my own. 



Following out the full history of the diagram I am carried back 

 more than twelve years. As long ago as 1888 my researches on lar- 

 val structures in fishes commenced. Their results in course of time 

 carried the investigator in the direction of the recognition of an anti- 

 thetic alternation of generations. Since that standpoint was attained, 

 no facts adverse to it have been encountered. The doctrine has never 

 been seriously attacked: it has been simply ignored. It has not as yet 

 won many adherents: the truth never does at first. For myself I have 

 been content to follow out the inquiry, and from time to time, as op- 

 portunity offered, to glean a few more facts, supporting this theory of 

 development. During part of this period a watch has been kept for 

 something equivalent to the formation of spore-mother-cells in the higher 

 plants or Metaphyta, but in vain. Hitherto, as at length clearly re- 

 cognised, the search had not been made in the right place. 



The investigator is often the creature of circumstances. These in 



