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



this formation of a spore mother-cell and of the embryo from the latter, 

 until my researches had revealed how she actually accomplished it. 

 No one could have been more astonished than the writer at the reve- 

 lation. Never had it for a moment been imagined, that the germ-cells 

 themselves would play the part they actually do in the life-drama of 

 an antithetic alternation of generations. Only when the work was 

 practically complete and ready for publication, was it seen, that the 

 missing link in the alternation had been discovered in the primary 

 germ- cells and in the epoch of their formation. 



I hardly feel called upon to prove that the primary germ-cells do 

 represent spore-mother-cells. If each of them were to undergo a re- 

 duction with the subsequent production of four ,,spores" ; and, if then 

 each animal spore were to develop into an organism, we should have 

 the exact equivalent of the gametophyte of one of the higher plants. 



Instead thereof they remain together, and only one becomes steri- 

 lised to form a sexual individual or gametozoon. Their remaining to- 

 gether and the continued and progressive amplification of the gameto- 

 zoon in course of ages have naturally deferred their ripenings, sex- 

 determinations, and reductions to later and later periods. It is obvious, 

 that this could easily be effected by starving them, but this may not 

 have been Nature's method of delaying their ripenings. A potent 

 factor has probably been delay in the period of the determination 

 of sex. 



In the higher plants it is the spores, whose name is legion, while 

 the ,,sexual cells", eggs and sperms, are few and far between. In 

 animals the ,,sexual cells" exhibit the reverse condition, corresponding 

 in their multitude to the spores of plants ; while, as we at length know, 

 the spore-mother-cells - - there are no spores in the Metazoa are 

 not very numerous, being represented in some cases by but one cell, 

 in addition to that which forms the sexual generation. 



Why this difference 1 )? In the embryo-sac of Pinus, which is the 

 gametophyte, there are only four germ-cells. In the corresponding structure 

 in flowering plants there are perhaps three, or at most six or eight; 

 while, as is well known, the male gametophyte of a flowering plant 

 is represented by one or two vegetative cells and one or two germ- 

 cells. 



No Metazoan sexual generation has so small and scant an 

 endowment as these, while such an animal may contain and harbour 

 a number of germ-cells thousands of times greater. 



1) ,,Zu vielen Tausenden zahlen die vegetativ erzcugten Sporen, welche 

 ein einziges Farnblatt ausstreut. Bei der geschlechtlichen Fortpflanzung der 

 folgenden Generation wird dagegen von eiuem Prothalliuni selten mehr als ein 

 neues Einzelwesen gebildet etc." F. Noll in Strasburger's B Lehrbuch der 

 Botauik", zweite Auflage, 1895, p. 255. 



