1 8 SSAYS SCIENTIFIC AND PHILOSOPHICAL. 



and hence only those characters can be transmitted through 

 successive generations which have been previously inherited 

 viz., those characters which were potentially contained in the 

 structure of the germ-plasm. It also follows that those other 

 characters which have been acquired by the influence of 

 special external conditions, during the lifetime of the parent, 

 cannot be transmitted at all." 



It is obviously impossible to attempt anything 

 like a criticism of Weismann's theory. Its evidence 

 lies almost exclusively in the domain of embryology, 

 and must be judged by professed embryologists. 

 A part of this evidence, to which we have not even 

 alluded hitherto, is Professor Weismann's theory 

 as to the nature and meaning of the polar bodies 

 given off by the unfertilized ovum in both plants 

 and animals ; a theory which, if it be generally 

 accepted, will not only be a valuable support to 

 Professor Weismann's main position, as explaining 

 the differences as well as the likenesses which exist 

 between the offspring of the same parents, but will 

 rank among the more important discoveries of 

 modern embryological science. 



But in reading these essays we cannot help feel- 

 ing, what was indeed a priori probable in a theory 

 which was diametrically opposed to Lamarckianism, 

 that too hard a line is drawn between the repro- 

 ductive and the somatic cells. To most people 

 it would seem that, however slight it may be, or 

 however slowly it may take effect, there must be a 

 reaction of the individual life on that of which it is 



