EFFECTOR SYSTEMS OF ACTINIANS 463 



Wolff ('04, p. 250) has described nerve fibers in connection 

 with the gland cells in actinians and von Uexkiill ('09 a) has 

 expressed the opinion that the secretion of mucus in these ani- 

 mals is under the control of their nervous mechanism. The fact 

 that on stimulation mucus is discharged only over the surface 

 stimulated and never beyond this area gives no support to this 

 view but suggests rather that this activity is due to local stimu- 

 lation unassisted by nervous action. This opinion is rendered 

 probable by experiments made on anaesthetized actinians. If 

 a Metridium that has been shown to secrete mucus on mechanical 

 or on stimulation by weak acid is put in seawater to which mag- 

 nesium sulphate has been added, the animal wall cease to respond 

 through its neuromuscular mechanism in about ten minutes. 

 Nevertheless it will discharge mucus freely but locally to ap- 

 propriate mechanical and chemical stimulation and this power 

 will remain in full vigor even after the animal has been in the 

 magnesium solution seven hours. Hence it would appear that 

 the secretion of mucus is not dependent upon nerves. 



Similar results were obtained from chloretone. After a 

 submersion of ten minutes in seawater containing chloretone, 

 Metridium ceased to respond through its neuromuscular mechan- 

 ism to mechanical stimulation. Notwithstanding, it secreted mu- 

 cus to appropriate local stimuh, and this recurred even after 6 

 hours of uimiersion in the chloretone seawater. From the obser- 

 vations already recorded and from the results of the experiments 

 on anaesthetization, I believe we are w^arranted in concluding 

 that the nervous system of actinians is not involved in calhng 

 forth the secretion of mucus but that this activity is accomphshed 

 by the direct stimulation of a body of independent effectors, 

 the specific gland cells of the ectoderm and entoderm. 



THE NE^IATOCYST SYSTEM 



No cellular constituents are more characteristic of any large 

 group of animals than the nematocysts are of the coelenterates, 

 for the occurrence of these organoids in certain mollusks seems 

 to be due to a process of digestive appropriation from ccelenterate 

 sources. The offensive and defensive chai'acter of nematocysts 



