THE VITAL PROPERTIES OF THE CELL 



changes of shape which an individual organ experiences as a 

 consequence of muscular action or of distension through a col- 

 lection of fluid or nutriment. Thread-like epithelial cells have to 

 become cylindrical, and cylindrical ones to become flat, when the 

 surface increases in size through the distension of an organ, 

 whilst, on the other hand, the reverse takes place when the 

 whole organ, including its surface, decreases in size. 



How powerful and sudden may be the changes of form which 

 the protoplasm of a cell, in consequence of passive movement, 

 may experience without damage to its delicate structure, can be 

 best seen in Ccelenterata, in which extended portions of the 

 body, like palpocils, may sud- ^ j> 



denly shorten by about a tenth 

 or more of their length, in con- 

 sequence of sudden energetic 

 muscular contraction (III. 12 

 a). The form which an epi- 

 thelial cell assumes varies very 

 considerably, according as to 

 whether it has been taken from 

 a portion of a body which is 

 moderately or strongly con- 

 tracted, as may be seen by 

 comparing Fig. 51 A, B. The 

 former was taken from the ten- 

 tacle of an Actinia, which was 

 only moderately contracted, 

 since by means of chemical reagents it had been rendered non- 

 sensitive before it was killed ; the second was derived from the ten- 

 tacle of another individual which had contracted strongly in death. 



FIG. 51. Muscular epithelial cell from the 

 endodermal surface of the tentacle of an 

 Actinia (Sagartta parasttrca) (tifier O. arid R. 

 Hertwijr, pi. vi., Fig. 1] ; from Hatschek, 

 Fig. 108): A extended condition of tentacle; 

 B strongly contracted condition of same. 



Literature III. 



DE BARY. Die Mycetozoen. Zeitschrift f. ivissenschaftl. Zoologie. Ed. 10. 



1860. 



2. G. BERTHOLD. Studien iiber Protdplasmamechanik. Leipzig. 1886. 



3. BtrrscHLi. Protozoen. First Volume of Bronn's " Classen und Ordnungen 



dfs Thierreichs." 1889. 



4. ALEX. ECKER. Zur LeJire torn Ban it. Leben der conlractilen Suhstanz der 



niedersten Thiere. Zeitschrift f. wissemchuftl. Zoologie. Bd. I. 1849. 



5. ENGELMANN. Protoplasm and Ciliary Movement, trans, by Bourne from 



Hermann's " Handbuch der Physioloyie." Bd. I. Quar. Jour. Mic. 

 Soc. 1880. 



