258 



One may say this, and at the same time freely acknowledge that, 

 in some respects, the views of Weismann have been distinctly 

 foreshadowed or overlapped by the statements of other biologists. 

 No one, however, has offered a theory so compact or so logicallv 

 €omplete in all its parts. 



A fresh interest in Weisraann's theories, now some few years 

 old, has been recently kindled by the publication of an English 

 translation of his writings by the Clarendon press ; but as his 

 elaborate system of biological j^hilosophy is there presented in a 

 series of disconnected essays, it is a matter of considerable diffi- 

 <3ulty, for those unfamiliar with biological methods of reasoning 

 and research, to gather up the thread of his argument which 

 runs through the whole series of separate articles. This being so, 

 I conceive that I may be of some service in offering to this 

 Society an epitome of the chief theories which comprise his system, 

 in such a form as to make its comprehension as easy as is possible 

 in a subject naturally full of difficulties. And I will take this 

 opportunity of acknowledging the great assistance I have received 

 in this task from the writings of Romanes, Shipley, Sir William 

 Turner, McKendrick, Vines, and others who have aj^peared either 

 as the advocates, opponents or interpreters of the views of Pro- 

 fessor Weismann. From these I have freely borrowed. 



Recent researches, especially amongst the Invertebrata, have 

 made it abundantly clear that the young animal arises by the 

 fusion, within the egg- or germ-cell, of an extremely minute par- 

 ticle derived from the sperm-cell produced by the male-parent 

 with an almost equally minute particle derived from the germ- 

 cell itself the product of the female-parent. These particles are 

 termed the male- and female-pronucleus respectively, and the re- 

 sulting body formed by their fusion the segmentation-nucleus, 

 wdiich, though exceedingly minute, is also exceedingly complex 

 both in its chemical and molecular constitution. 



From this segmentation-nucleus and from the surrounding 

 protoplasm of the egg-cell other cells arise by a process of sub- 

 division, and these at length become arranged in definite layers, 

 called the germinal layers, from which all the tissues and organs 

 ■of the body are gradually formed in orderly sequence. It is the 

 segmentation-nucleus which thus forms the starting point of all 

 the subsequent complicated changes; and inasmuch as this is 

 formed by the fusion of particles of material from both parents 

 w^e start with the fact of a physical continuity between parent 

 and offspring, and are thus enabled to lay down are fundamental 

 proposition that a physical basis for heredity exists. 



One result of this physical continuity of substance is that the 

 offspring resembles the parents not only in bodily form and 



