II. 

 Hertwig's " Preformation or New Formation." ' 



Part II. — Criticism of Weismann's Theory of the 

 Germ-plasm and Doctrine of Determinants. 



ALTHOUGH Weismann has carried out his theory into the 

 greatest detail, it is not with details so much as with the 

 fundamental principles of it that Hertwig disagrees. It is with these 

 principles, as they concern what is known about cells, that the chief 

 difficulties seem to him to occur. No doubt, as Naegeli has said, 

 there are many units of different orders above and below the cell, but 

 the observation of the last thirty years has made it more and more 

 certain that the cell is the most striking morphological and physio- 

 logical unit of the body. Every theory of heredity must be tested 

 by comparing it with facts observed about the cell. The cell, con- 

 sisting of protoplasm and a nucleus, is an elementary organism, 

 which, by itself or in combination with others, forms the basis of all 

 organisms. It has an inconceivably complex structure, which, in its 

 minuter parts, eludes our observation, and it is composed of many 

 physical substances. Of these, albuminates, fats, carbohydrates, 

 water, salts free or in solution, serve as material for the growth of 

 the cell. Others form the living cell-body, in the narrow sense : 

 by growth and division they can multiply and form the elementary 

 unit of which the cell is a higher combination. In this category of 

 intra-cellular units would be placed, if they existed, such theoretical 

 structures as the gemmules of Darwin, the physiological units of 

 Herbert Spencer, the bioplasts of Altmann, the pangenes of De 

 Vries, the plasomes of Wiesner, the idioblasts of O. Hertwig, and 

 the biophores of Weismann. The cell of each species has its specific 

 organisation of a simpler or more complex structure, and contains a 

 proportional number and variety of organised lower units. An un- 

 failing organ of every cell is the nucleus, which is composed of elemen- 

 tary living units, the idioblasts, which differ chemically, morphologi- 

 cally, and physiologically from the units of the protoplasm, but may, 

 perhaps, be able to turn into them. As a matter of observed fact, the 



1 Zeit- und Streitfragen der Biologie. By Professor Dr. Oscar Hertwig. 

 Pamphlet I. Praeformation oder Epigenese ? Grundzuge einer Entwicklungs- 

 theorie der Organismen. Pp. 144, with 4 illustrations in the text. Jena : Gustav 

 Fischer, 1894. Price 3 marks. 



