446 



PHYSIOLOGY. 



muscular layer, which, by means of compression and distension, produce 

 a certain change in the compass of the vegetative organs, which partly 

 contracts them and partly allows them to relapse to their former com- 

 pass, and that it is only in consequence of this motion that the functions 

 of every individual part and organ can proceed uninterruptedly. These 

 motions are especially visible in the several parts of the nutritive 

 system, Avhere they present themselves as the peristaltic motion of the 

 intestinal canal, as the respiratory motion of the tracheae, and, lastly, 

 as the pulsations of the heart. All these motions have been described 

 sufficiently in detail in a former chapter, where we have spoken of the 

 functions of the nutrimental system, and where we discerned in them 

 the true cause of the entire process of nutrition, which commences with 

 the reception of the food. The motions of the sexual organs are less 

 apparent, as they become visible only at certain periods. Yet in the 

 male sex there appears to be, from the moment of puberty, an undis- 

 turbed production of semen. This semen, by means of a motion not 

 dissimilar to the peristaltic motion of the intestine, arrives in the vesica 

 semmalis, whence it passes during copulation into the female organs. 

 After this act the activity of the female organs commences, which 

 exhibits itself as a peristaltic motion, both in the egg-tube and in the 

 oviduct, and where it terminates in the production of the collective 

 egg germs. 



Upon surveying the common expression of all these motions, we 

 recognise nothing further in them than a spontaneous re-action on the 

 part of the organism to external irritation at least, external in reference 

 to the organ which is moved. This irritation consists in the food, for 

 the intestinal canal, the atmospheric air for the tracheae, the blood 

 for the heart, the semen secreted by the testes for the male organs, 

 and for the female organs the male semen also which is conveyed into 

 them. 



262. 



The stimulus, however, which determines the action of the voluntary 

 muscles is the will only of the creature ; the insect has but to will, and 

 in the same moment its legs are in motion, and it flaps its wings and 

 hastens away. The common property of both, therefore, consists in 

 their requiring a medium of irritation, the differences we find in the 

 phenomena are that this excitement for the involuntary muscles is 

 physical and corporeal, and that for the voluntary is spiritual. Both 



