EFFECTOR SYSTEMS OF ACTINIANS 465 



in length and consist of a spirally marked, basal stalk some 

 70ai long and a terminal filament of over 700/i length, the total 

 extent of these elements being at least twenty-five times that 

 of the shortest netthng organs in this animal. 



To ascertain the relation of the nematocysts to the nervous 

 system in actinians the following experiments were carried out 

 on the tentacles and the acontia of Metridium. A normal 

 acontium can be cut from an animal and placed under a micro- 

 scope without bringing about the discharge of its nematocysts. 

 If, now, it is flooded with carmine in seawater or with a solution 

 of methylene blue in seawater, its ciha can be seen to strike 

 toward what was its distal end, but no nematocysts will be ex- 

 ploded. If, next, it is flooded with HCl -, a profuse discharge 



of nematocysts occurs. Judging from the observations of Glaser 

 and Sparrow ('09) probably most acids would cause this reaction. 

 Distilled water will also bring about the explosion of the nema- 

 tocysts, but as a rule only a few are thus discharged, for, if the 

 treatment with water is followed with dilute acid, a renewed 

 discharge immediately takes place. Some samples of methyl 

 green have been found to produce a very complete explosion 

 of the nematocysts but others have not, a fact which indicates 

 that the discharge was probably produced by some associated 

 impurity rather than by the methyl green itself. A few nema- 

 tocysts are always discharged near the cut end of the acontium, 

 and if an acontium is shot in and out a pipette in seawater, many 

 of the nematocysts will be found discharged. These organoids, 

 however, are not exploded when the acontium is flooded with 

 juice from the flesh of a fish (Fundulus) though they do discharge 

 in fair numbers when a small piece of this flesh is brought into 

 contact mth them. This reaction is probably dependent upon 

 a mechanical rather than a chemical stimulus from the flesh. 



The tentacles of Metridium discharge their nematocysts to 

 dilute acids, certain samples of methyl green, mechanical insult, 

 and more or less to distilled water but not to carmine nor methylen 

 blue nor to meat juice in seawater. In fact the nematocysts 

 of the tentacles respond to the various stimuli I have tried in 

 precisely the same way as those of the acontia do, and I have 



