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 theory 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 body 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 with the apparatus ; 
and for this reason a sketch like the above removed from the com- 
