176 REPORT —1891. 



buted the whole evolution of organic nature to these influ- 

 ences ; and Darwin attaches not a little weight to them in 

 Bome parts of his work. It is especially on this question — the 

 question of the inheritance of acquired characters, — and on that 

 just mentioned — the question of the mode of origin of varia- 

 tions, — that there has been of late a considerable reawakening 

 of interest in theories of evolution. Ever since the publication 

 of Weismann's Addresses this discussion has been going on, 

 but in English-speaking countries the interest in the matter has 

 become more general since the publication last year of an 

 English translation of Weismann's essays on this and cognate 

 subjects, so that during the last year a large number of papers 

 and articles dealing with Weismann's views have appeared in 

 the various scientific periodicals, as well as in the reviews and 

 magazines. 



Weismann, as every one now knows, sets himself in oppo- 

 sition in some points to Darwin, and in all, as far as concerns 

 evolution, to Lamarck. According to the Freiburg professor 

 acquired characters never are, and, from the nature of the case, 

 cannot be, transmitted by inheritance ; so that the results of 

 individual experience can have nothing to do with the develop- 

 ment of organisiiis. Any changes, in other words, which arise 

 in the individual as a result of the action of external conditions 

 or of individual effort are incapable of being transmitted to the 

 offspring. This follows as a necessary result from a remark- 

 able dogma which Weismann calls "the continuity of the 

 germ -plasma." 



In the egg-cell, as in other cells, the most essential part is 

 the nucleus. The great importance of the nucleus in the life 

 of the cell has long been a matter of deduction from many ob- 

 served facts. More recently experiments made by Gruber and 

 Nussbaum on the Infusoria have demonstrated that the nucleus 

 is the part in which resides the central controlling force of the 

 cell, and in which resides its capacity for reproduction. In the 

 germ-cell, according to Weismann, the nucleus is the essential 

 part ; the protoplasm of the body of the cell is, for the most 

 part, merely nutritive in its functions.''' This essential sub- 

 stance then of the germ-cell is, according to Weismann, con- 

 tinuous from generation to generatioia : that is to say, the 

 essential substance of one generation of germ-cells is derived, 

 and can only be derived, from the essential substance of the 

 germ-cells of the preceding generation. Germ-plasma cannot be 

 formed from the protoplasm of histologically differentiated cells; 

 it must be derived from the plasma of pre-existing germ-cells. 



* This, it is to be noted, is not universally admitted. See a paper by 

 Whitman " On the Seat of Formative and Regenerative Energy " in the 

 "Journal of Morphology," Vol. 2. See also the work of de Vries, referred 

 to further on. 



