IX THE HISTORY AND SCOPE OF ZOOLOGY 359 



tion (1 759) maintained that the germ is a structureless 

 particle, and acquires its structure by " epigenesis " 

 or gradual development. Wolff has proved to be 

 nearer the truth than Haller ; but modern conceptions 

 as to the molecular structure of the egg-protoplasm 

 point to a complexity as great as that imagined by 

 the evolutionists. Later it was maintained that the 

 spermatozoa are parasitic animalcules, and this view 

 prevailed for 150 years, so that in the Physiology of 

 Johann Miiller (1842) we r'ead, " Whether the sperma- 

 tozoa are parasitic animalcules or living parts of the 

 animal in which they occur cannot at present be 

 stated with certainty." 



Physiology in the eighteenth century could only 

 proceed by means of inferences from purely anatomical 

 observation, aided by imaginative conceptions which 

 had no real basis. The explanation of the processes of 

 life in the animal body was waiting for that progress 

 in the knowledge of physics and chemistry which at 

 last arrived, and gave a new impulse to investigation. 

 Albrecht von Haller (1708-1777) was the first to 

 apply experimental methods to the determination of 

 the functions of the various organs made known by 

 anatomists, and from him we may trace a bifurcation 

 in the tendencies of medical men who occupied them- 

 selves with the study of the structure and functions 

 of the animal organism. The one class proceeded more 

 and more in the direction of comparative anatomy, the 

 other in the direction of exact analysis and measure- 

 ment of both the structure and properties of the organs 

 of Vertebrate animals allied to man and of man himself. 



