Beard, Heredity and the epicycle of the germ-cells. 405 



The difference is solely due to the different procedure adopted at 

 the formation of the primary germ-cells or spore-mother-cells. The 

 plan carried out in animals has been such as to favour and foster the 

 ever greater and greater amplification of the sexual generation. In 

 plants, as elsewhere already insisted, the reverse is the case. Here 

 the asexual generation has undergone increased amplification without 

 ever being able to attain any very high degree of histological differen- 

 tiation. The sexual generation of plants is at the best a miserable 

 failure from the morphological point of view, and this must be set 

 down to the factors already indicated. 



The higher one ascends the smaller it becomes, until in the 

 highest flowering plants it has almost reached the vanishing point, 

 without, however, being able to disappear entirely. 



In animals it is the larva, the phorozoon, or asexual generation, 

 which makes the bravest show in the lower Metazoa; but even here 

 it is always overshadowed in degree of morphological differentiation 

 by the ,,embryo" or sexual generation. In the higher forms it becomes 

 reduced; but, like the rudimentary sexual generation of the higher 

 plants, it cannot vanish, for it also has its assigned task in the repro- 

 ductive round, and in the Metazoa ,,direct development" is as much 

 an impossibility as epigenesis or the formation of germ-cells from so- 

 matic cells! 



The sexual generation or gametozoon, thanks to the importance of 

 the precious cargo of germ- cells, which it carries, has received the 

 kindly attentions of Nature, with consequent higher and higher evo- 

 lution. From a variety of causes the larva or phorozoou, on the other 

 hand, tends to simplification the higher one ascends. At the best its 

 organisation is simple, but even this simplicity leans to meagreness in 

 the Vertebrata as they now exist. 



With the formation of the primary germ- cells the next item in 

 the life- cycle is the production of an embryo or sexual generation by 

 the self sacrifice of one for the good of the rest. This is indicated in 

 the diagram as having fallen to the lot of the 37th germ-cell from 

 the bottom. 



In the skate the embryo at first contains no germ-cells, and the 

 primary germ-cells enter it as such: but, and this is another of the 

 facts established by my work, by the time the embryo is completely 

 laid down, the primary germ-cells divide and form secondary ones. 

 So that, as a rule, by the time the evolution 1 ) of the embryo is over 



1) The word ,,epigenesis tt is here deliberately avoided. After very pro- 

 longed study of the mode of vertebrate development my conclusion is, that 

 epigenesis has no existence. In the preface to his n Germ-plasm u Weismann 

 writes ! finally became convinced that an epigenetic development is an im- 

 possibility. Moreover, I found an actual proof of the reality of evolution etc." 



