ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 305 



Movements of Tentacles in Actinians.* — G. H. Parker has studied 

 the well-known power that the tentacles of sea-anemones have of carry- 

 ing out many of their normal activities even after they have been cut 

 from the body of the polyp. This peculiarity has been accepted as 

 evidence that each tentacle contains a neuro-muscular arrangement 

 sufficient for its own activity, and that it is therefore not dependent 

 upon the nervous control of other parts of the animal's body for the 

 production of those movements that it ordinarily exhibits. To test the 

 validity of this view experiments were made on 3Ietridium marginatum, 

 Sagartia luciee, and Condylactis passiflora, the last being most suitable 

 because of the large size of its tentacles. 



A. severed tentacle of Condylactis, suspended in sea-water by a small 

 metal hook, may be inflated by running water into it until it has attained 

 about two-thirds of its natural length. It then has a fluid-pressure very 

 nearly that which was natural to it, and not greater than a few milli- 

 metres of water. If this be much increased the tentacle contracts 

 vigorously and discharges much of the contained water. The slightly 

 contracted state of the expanded, excised tentacle is not due to lack of 

 pressure, nor to the absence of inhibitory influences from the rest of the 

 polyp, but to the cut at its base, which increases the tonicity of its neuro- 

 muscular arrangements. 



Excised tentacles stimulated by mechanical means, by food, or by 

 chemicals, react in essentially the same way as attached tentacles do, 

 though the reactions are feebler and less precise. Stimuli applied to 

 the ectoderm of a tentacle are followed quickly by a muscular response ; 

 appHed to the endoderm they are followed slowly by the same form of 

 response. This means that the endodermic surface is not receptive, and 

 that stimulating substances applied to it make their way only slowly to 

 the ectoderm. If there is a nervous layer in the endoderm of the 

 tentacles of Condylactis it must be extremely simple in structure and 

 function, as compared with that in the ectoderm. 



The tentacles of Condylactis through their reactions exhibit marked 

 polarity, both ciliary and neuro-muscular. The latter disappears on 

 narcotization with chloretone. It is probably dependent on the direction 

 taken by the nerve-fibrils which emerge from the sense-cells. Where 

 this direction has been determined it is predominantly towards the 

 proximal end of the tentacle. 



The general conclusion is that " the Actinian tentacle, in contra- 

 distinction to such appendages as those of the Arthropods or the 

 Vertebrates, contains a complete neuro-muscular mechanism by which 

 its responses can be carried out quite independently of the rest of 

 the polyp." 



Pedal Locomotion in Actinians. f — G. H. Parker finds that the 

 direction of creeping in Actinians is independent of their secondary axis. 

 In a single specimen of Actinia or Sagartia the direction may change 

 from time to time without relation to the secondary axis. The bi- 

 laterality of Actinians, therefore, is not locomotor as in most animals. 



* Journ. Exper. ZooL, xxi. (1917) pp. 95-110 (1 fig.), 

 t Journ. Exper. ZooL, xxi. (1917) pp. 111-24 (1 fig.). 



