326 'Journal of Comparative Neurology and Psychology. 



so that this part rospoiids when any })ai't of the Ixxly is stimiihitcih 

 This part to which tonus flows as water flows into a valley is 

 denominated, with poetic feeling, the vale of tonus ("Tonustal," 25, 

 p. 310; 29, -[). 50). After the tonus has flowed into certain muscles, 

 it is possible (in some cases at least) to capture and hold it there, 

 by cutting the ner^'es leading to the muscles (''Tonusfang/" 25, p. 

 302) ; the muscles then remain contracted. 



During rest the fluid tonus is gradually used u}) and disa})pcars; 

 at stimulation it is newly manufactured. There exist, however, 

 reservoirs of tonus in the nervous system, so that the lost tonus 

 of the muscles can be replaced without new manufacture. 



The nervous system then contains, besides a system of communi- 

 cating tul)es, reservoirs of tonus; at the same time it is an elaborate 

 apparatus for controlling the distribution of tonus. Each muscle 

 has somewhere in the nervous system an organ which is its "repre- 

 sentative" (25, p. 303; 29, p. 44). The ofHce of this representative 

 is to see that the tonus ])ressure in the muscle remains sufficient to 

 cause the tension of the muscle to correspond to the weight which it 

 has to bear. When the pressure in the muscle is insufficient, this 

 acts on the representative (through the nerve) causing it to increase 

 the pressure, until this raises the tension so as to sup])ort the weight. 

 The increased ])ressure is produced by the fact that the representative 

 uses up a certain quantiiy of tonus to increase the pressure of what 

 is left. 



The author's further development of this system consists in work- 

 ing out in detail the structure and action of this system of tubes, 

 reservoirs and other nuu'hinery, by which the distribution of tonus 

 is controlled. ]\rain tubes, feeders, reservoirs, valves, etc., are de- 

 vised and represented by diagrams, till we finally get figures which 

 resemble the plan for a dye-w'orks or a flour mill (see for example 

 the schema for Sipunculus, 25, Tafel 6). 



The method of ])resentation is in general the ideal construction 

 of an a]iparatus which could produce the results shown by the 

 organisms. In this construction no attempt is made to represent 

 apparatus that actually exists in the organism ; it is merely a figure or 

 illustration ; "a mere schema in accordance with which one can group 



