90 BEHAVIOR OF THE LOWER ORGANISMS 



A discharge of trichocysts is produced by many different agents. 

 The trichocysts are rodlike sacs in the ectosarc, perpendicular to the 

 outer surface. Their contents are ejected, under certain conditions, into 

 the water, forming long threads. According to some authors, these 

 threads have a definite structure, and are probably preformed within 

 the animal. Others suppose the threads to be formed by the coagula- 

 tion of a fluid contained within the sacs. After discharge of the tricho- 

 cysts the animal appears to be surrounded by a zone of radiating fibres 

 (Fig. 65). 



The discharge of trichocysts under the influence of stimuli has been 

 studied especially by Massart (1901 a), and by Statkewitsch (1903). 



Crushing the animal causes 

 discharge of trichocysts in 

 the region injured. Weaker 

 mechanical stimuli do not 

 have this effect. If the ani- 

 mal is heated rapidly till it 

 is killed, it discharges the 

 trichocysts before dying; if 



FIG. 65. Paramecium with trichocysts discharged, heated slowly, this effect is 

 the application of picric acid. ^ produced> Ne i t her Cold 



nor increased osmotic pressure have any effect on the trichocysts. Many 

 chemicals produce the discharge, particularly various acids. Saturated 

 solution of picric acid causes a sudden discharge of all the trichocysts at 

 once. One-fourth per cent methylene blue produces a slow and irregular 

 discharge successively from different parts of the body. 1 If any agent 

 acts on a limited portion of the body surface, the trichocysts of only that 

 region are discharged. Many chemicals kill the animal without dis- 

 charge of the trichocysts. 



A weak induction shock causes discharge of the trichocysts at the 

 anode only (Fig. 60) ; a stronger shock causes discharge at both anode 

 and cathode. A still stronger shock causes discharge of the trichocysts 

 over the entire surface of the body (Statkewitsch, 1903). 



In the discharge of the trichocysts we have a phenomenon compara- 

 ble to the definite reflex actions observed in various organs of higher 

 animals. The function of the trichocysts is uncertain. They are usu- 

 ally supposed to be weapons of defence. If the Paramecium is seized 

 by an animal which is attempting to prey upon it, the trichocysts will of 

 course be discharged from the injured region. But whether they really 



1 To demonstrate the discharge of the trichocysts it is convenient to use picric acid 

 alone or picric acid to which a little aniline blue has been added. In the latter case the 

 trichocysts become colored blue (Massart). 



