SYLLABUS OF LECTURES IN THEORET- 

 ICAL BIOLOGY. 



SUPPLEMENT, J 897. 



The following section may he substituted for the corresponding one in the 

 text, pages 17 to 27. 



iv. Theories of Heredity and Development. 



(For list of references see page 17.) 



1. Importance of the subject. 



2. Requirements of a theory of heredity. 



It must include a theory of variation. 



It must inckide a theory of development in the 

 deepest sense. 



It must explain all the phases of development. 



It involves some conception of the essential struc- 

 ture of living matter. 



3. The fundamental conceptions in theories of heredity. 



4. Animism. 



Van Helmont (i 577-1644). 



5. Physiological units. 



BuFFON (1 720-1 793), organic molecules. 



Spencer (1864), physiological units. 



Haeckel (1876), plastidules. 



Weismann (189 1, 1893), biophors, determinants. 



Nageli {1884), micellae, micellar threads. 



Darwin (1868), gemmules. 



De Vries (1889), pangenes. 



BuTCHLi (1892), Andrews (1897), protoplasmic 

 foam. 



