66 MOTIONS OF SPERMATOZOA. [CHAP. II. 



frog, the closed cavities of the pericardium and peritoneum. Here 

 there are no excretory orifices, toward which the current might set. 



What is the cause of ciliary motion? "We have shewn it to 

 be independent of the blood and of the nerves, and to resist those 

 depressing causes which usually put a stop to the action of con- 

 tractile tissue. It requires for its continuance three conditions : 

 a perfect epithelium cell ; moisture, not of too great density ; and 

 a temperature within certain limits. From Schwamr's observations 

 it appears that cells exhibit a power of endosmose ; that a chemical 

 change occurs in the fluids in contact with them ; and that a move- 

 ment of their internal granules may be seen under certain circum- 

 stances. If ciliated epithelium cells exert an attraction of endos- 

 mose upon the surrounding fluid, may not this physical phenomenon 

 afford a clue to determine the cause of the movement ? 



A very remarkable movement is manifested by certain particles 

 found in the secretion of the testicle, which prevails most exten- 

 sively throughout the animal series, and is even found among plants. 

 From the regularity of these movements, and their resemblance to 

 those of minute animals, a place had been assigned by naturalists 

 to the particles in question, in their zoological classifications, under 

 the name " Cercarice, seminis" Spermatozoa, or Spermatic ani- 

 malcules, and Ehrenberg refers them to the Haustellate Entozoa. 

 These particles consist chiefly of a long filament or tail, which is 

 sometimes swollen at one extremity, to form the body of the sup- 

 posed animalcule. The motions consist in a sculling action of the 

 tail, or a slight lateral vibration of it. In many of its conditions 

 it closely resembles ciliary motion ; and its duration after death, or 

 after the separation of the fluid, is pretty much the same as that of 

 the ciliary movements. The particles are extremely minute, even 

 measured in their length; but especially so in thickness. They are, 

 therefore, well adapted to obey those impulses which we have 

 shewn to be capable of giving rise to molecular motions. We shall 

 return to this curious subject again in discussing the function of 

 generation. 



On the subjects treated of in this chapter reference is made to the follow- 

 ing sources of information : Eob. Brown, A Brief Account of Microscopical 

 Observations on the particles contained in the pollen of plants, and on the 

 general existence of active molecules in organic and inorganic substances ; 

 Purkinje and Valentin, Comment atio Physiologica de phenomeno motus vibra- 

 torii continui ; article Cilia, by Dr. Sharpey, in the Cyclopaedia of Anatomy 

 and Physiology ; Valentin's article Flimmer-bewegung in Wagner's Hand- 

 worterbuch cler Physiologic. 



