OTHER FORMS OF CONTRACTILE TISSUE 277 



In the invertebrata many ' voluntary ' striated muscles probably possess 

 a double innervation. Thus in the crayfish the adductor muscle of the claw 

 consists of striated muscular fibres, every fibre of which is supplied with two 

 kinds of nerve fibres. By exciting these fibres 

 one may get, according to the conditions of the 

 experiment, either contraction of a relaxed 

 muscle or relaxation of a tonically contracted 

 muscle (Fig. 99). 



AMOEBOID MOVEMENT 



Amoeboid movement is seen in the 

 unicellular organisms such as the amoeba 

 and in the white blood corpuscles. It can 

 occur only within certain limits of tem- 

 perature (about C. to 40) ; within these 

 limits it is the more active the higher 



600 



] 



FIG. 99. Tracing of contraction 

 of adductor muscle of claw 

 of crayfish, showing inhibi- 

 tion resulting from stimula- 

 tion of its nerve (at b) by 

 means of a constant current. 

 The break of the current 

 causes a second smaller in- 

 hibition. (BlEDERMANN.) 



the temperature. At about 45 the cell 

 goes into a condition resembling heat 

 rigor. 



The fluid in which the corpuscles are suspended is of great 

 importance. Distilled water, almost all salts, acids and alkalies, if 

 strong enough, stop the action and kill the cell. 



The movements are also stopped by C0 2 or by absence of oxygen. 



Artificial excitation, whether electrical, 

 chemical, or thermal, causes universal con- 

 traction of the corpuscle, which therefore 

 assumes the spherical form. 



CILIARY MOVEMENT 

 Cilia are met with in man in nearly the 

 whole of the respiratory passages and the 

 cavities opening into them in the genera- 

 tive organs, in the uterus and Fallopian 

 tubes of the female, and the epididymis of 

 the male, and on the ependyma of the 

 central canal of the spinal cord and its 

 continuation into the cerebral ventricles. 



The cilia (Fig. 100) are delicate taper- 

 ing filaments which project from the hyaline 

 border of the epithelial cells. There are 

 about twenty or thirty to each cell. The 



hyaline border is really made up of the enlarged basal portions of 

 the cilia. 



In action the cilia bend suddenly down into a hook or sickle form, 

 and then return more slowly to the erect position. This movement is 



FIG. ICO. Ciliated columnar 

 epithelium from the trachea 

 of a rabbit; m l , m 2 , m 3 , 

 mucus-secreting cells. 



(SCHAFER.) 



