400 INTRODUCTION TO CYTOLOGY 



tive protoplasm, or trophoplasm, the micellae have no regular orienta- 

 tion, whereas in idioplasm they are oriented in a particular manner. 

 According to Nageli the phenomena of heredity are due to the constitu- 

 tion and transmission of this idioplasm; idioplasm is the physical basis of 

 inheritance. It is not confined to the nucleus, but forms an elaborately 

 constituted network extending throughout all the cells of the organism. 

 By arranging themselves in various groupings within this network the 

 micellae are able to bring about the development of the many specific 

 characters. The further details of this highly "fragile" hypothesis are 

 summarized in convenient form by Delage and Goldsmith (1913), who 

 point out that in spite of its many unsupported assumptions it did involve 

 two fertile ideas: first, that there are two kinds of protoplasm, one of 

 which carries the characters of the organism; and second, that there are a 

 limited number of elementary characters which combine in various ways 

 to produce the many visible characters. 



Weismann's Theory. — The most highly developed and influential of 

 all such speculative theories was that of Weismann. On the basis of the 

 conception of pangens Weismann built up the highly involved system 

 of hypotheses set forth in his Das Keimplasma of 1892 and in more 

 elaborated form in his Evolution Theory of 1902. Certain modifications 

 were later made. 



As Delage and Goldsmith have noted, Weismann incorporated in his 

 theory several of the stronger points of earlier theories, such as Darwin's 

 conception of representative particles, Nageli's elementary characters, 

 and de Vries's intracellular migration of particles. With Nageli he dis- 

 tinguished between nutritive morphoplasm and hereditary idioplasm or 

 germ-plasm, but unlike Nageli he identified the idioplasm with the 

 chromatin of the nucleus. His conception of the constitution of the 

 idioplasm was essentially as follows: 



The ultimate unit in all living matter is the biophore, which is a 

 minute living particle capable of growth and reproduction — a vital unit. 

 The many kinds of biophores in a given cell represent the many characters 

 of that individual cell: they are not bearers of the characters as such 

 (though Weismann often spoke of them in this fashion), but are rather 

 factors upon whose presence the development of the characters depends. 

 The biophores are grouped to form vital units of a higher order, known as 

 determinants. The determinant, since it is composed of the many kinds 

 of biophores in the cell, has the power of determining the development of 

 a certain type of cell or group of cells. In general, therefore, there are as 

 many sorts of determinants in the organism as there are types of cells, 

 or " independently variable parts," to be developed. The determinants 

 are in turn grouped into ids. A single id contains all the kinds of deter- 

 minants, and so stands for the sum of all the characters of the organism: 

 it contains the "complete architecture' 1 of the germ-plasm. The ids 



