132 J. PAUL VISSCHER. 



thrown out with considerable force and the poison which they 

 contain is strong enough to paralyze any single-celled opponent." 



Minchin ('12) maintained that "the nature and mechanism of 

 (the peculiar) trichocysts still remains to be explained," but de- 

 scribed as typical those forms found in Paramecium and Front onia. 



Concerning the function of trichocysts there seems to be even 

 less known than there is about the structure. Jennings ('06) 

 wrote that trichocysts "are usually supposed to be weapons of 

 defense, but whether they really serve for defense seems question- 

 able," and suggested that their discharge may be only an expression 

 of injury "a purely secondary, even pathological phenomenon, 

 like the formation of vesicles on the surface of an injured speci- 



men." 



Mast ('09), however, showed clearly that in Paramecium the 

 trichocysts have a definite protective function. He observed that 

 the trichocysts of Paramecium are discharged in response to in- 

 jury, produced by Didinium, and that as soon as these trichocysts 

 come in contact with the water they form a mass having a firm 

 jelly-like consistency which serves to force the enemy back me- 

 chanically, and frequently results in setting the victim free. Cal- 

 kins ('10, p. 27) says that "sometimes they are used as weapons 

 of offense as well as protective organs," and in another place he 

 describes predaceous protozoa as " usually armed with offensive 

 organs in the form of trichocysts which may be shot out from the 

 surface of the body or carried javelin-like at the extremities of 

 projectile tentacles." 



A. .OBSERVATIONS ON THE NATURE AND THE FUNCTION OF THE 



TRICHOCYSTS OF Dilcptus. 



Numerous experiments and observations were made on Dileptus 

 to ascertain, if possible, the function as well as the structure of 

 the trichocysts, all of which, as previously stated, are located on 

 the oral surface of the proboscis. A description of a few of the 

 more illuminating of these experiments will follow, but before con- 

 sidering these we may briefly recall a few of the results of the 

 observations on feeding which have a bearing on this subject. 



Euglcna, it will be recalled, is paralyzed as soon as it comes in 

 contact with the oral surface of the proboscis, and after a short 



