64 Proceedings of the Royal Physical Society. 



generation takes its origin from one or more cells, as an 

 outgrowth on or in the original creature, while in others, 

 from time to time, a series of destructive and reconstructive 

 processes, termed metamorphosis, occurs, causing great 

 changes in the morphology and physiology of the animal. 

 In these outgrowths, gametes, in time, are formed, and 

 have been found, in some instances, to have wandered 

 into the new growth from the older type. An inclusion 

 of the germinal material also takes place in these forms 

 where the destructive and reconstructive metamorphosis 

 obtains. 



In comparing animals with plants, there should occur 

 a time in the life cycle of the former, when the homologues 

 of spores are formed, these giving rise, after a number of 

 divisions, to the conjugating gametes. There is, at present, 

 no definite point which can be fixed upon as homologous in 

 this respect, and authorities seem to differ as to the stage in 

 which reduction takes place. It is noteworthy that when, 

 in animals, a generation which bears gametes occurs as an 

 outgrowth on a former generation, although the other cells 

 of the body are capable, in some degree, of regeneration, no 

 buds are thrown off which can exist independently. It 

 would seem then that, in these cases, a certain degree of 

 sterilisation is imposed on this generation from its very 

 beginning, and that the cells in it which produce the gametes 

 have found their way into it by migration from the parent 

 form. Dr Beard, in his embryological researches, has come 

 to the conclusion that the cells which go to form the gametes 

 in the mammal, wander into the embryo from the tropho- 

 blast, and in the fish from the yolk-sac and blastoderm, and 

 these he looks upon as an older generation, upon which the 

 embryo has come to lead, for a time, a parasitic existence (2). 

 There seems good reason for having faith in this origin of 

 the germ cells in the higher animals, as it seems the most 

 easily understandable method of explaining how continuity 

 of germ cells can take place. From what is known of the 

 power of regeneration, it at first seems unnecessary to con- 

 sider that all the cells of the embryo must be destined for 

 sterilisation. So long as division of the cells continues, a 



