462 NATURAL SCIENCE. June. 



rate pieces Weismann names " ids," and suggests that the facts of 

 inheritance might be accounted for if each id contained the possibility 

 of producing the individual. On such a hypothesis Weismann shows 

 most ingeniously and convincingly how the observed marshalling and 

 sorting, division and rejection of idants and ids would form a 

 mechanical apparatus compatible with the complex phenomena of 

 inheritance to be accounted for. The next stage of his theor}' still is 

 along the path of observation. A certain number of idants with the 

 contained ids remain unused in each individual development. Occa- 

 sionally, but rarely, they are passed at once into a cell which becomes the 

 future mother sperm or mother ovum cell, and so the sperm-cells and 

 egg-cells of the individual arise directly from the idants present in 

 the fertilised egg-cell. More frequently, however, the set of idants 

 and ids are handed on passively from cell to cell during the develop- 

 ment of the individual, until they ultimately reach the place in the 

 individual where the sexual cells are to be formed. This path of the 

 germ-plasm he calls the " germ-track," and, as will be remembered, 

 it was his original hitting upon such germ-tracks in the 

 Hydrozoa that led him to suspect the existence of a germ-plasm. 

 Turning again to that part of the germ-plasm which is to form the 

 actual individual, we come to entirely theoretical matter. It consists 

 of ids, and each id contains the possibility of a complete individual. 

 The id is not a structureless substance, but possesses a definite 

 historical architecture— the expression of the past history of the 

 species. Each id is built up of smaller units, the " determinants," 

 and there is a " determinant " for each cell or group of cells in the 

 animal or plant bod}^ which can vary independently. As develop- 

 ment goes on the ids gradually break down, throwing off in the order 

 determined by their historical architecture the determinants to rule 

 the structure of the "determinates" or independently varying parts 

 of the organism. Thus ultimately we come to determinants passed 

 during cell-division into their appropriate cells. In these cells the 

 determinants break down into the final units or " biophors " which 

 pass through the nuclear membrane into the protoplasm of the cell. 

 Thus the "idioplasm" or chromatin derivative which rules the cell 

 consists of Weismann's theoretical determinants, and it rules the 

 cell by the passage of actual material particles into the protoplasm. 

 These biophors — the ultimate units of the germ-plasm — are, at the 

 same time, the primitive units of life, and Weismann conceives life as 

 having originally consisted of independent biophors. 



For each of the units of the germ-plasm Weismann postulates 

 the common property of living material, the power of growth and re- 

 production by division. This has of course been observed in " idants " 

 and is a ready inference for " ids." 



It is to be noted that a number of ids, each with the complete 

 power of producing an individual, are present in the development of 

 an individual. Thus there comes about the struggle between the 

 determinants and biophors coming from ids with slightly different 

 peculiarities, and thus the particulate variability of the parts of an 

 organism and the particulate resemblances to parents and ancestors 

 have a possible material apparatus. 



As the whole volume consists of a subtle and ingenious translation 

 of biological phenomena into the terms of this theoretical apparatus, 

 it is obvious that only a study of the book can give an idea of the 

 exactitude with which the phenomena correspond witli the apparatus ; 

 and for this reason a sketch like the above removed from the com- 



