BEHAVIOR OF SEA-ANEMONES. 283 



1. It seems clear that in the behavior of actinians toward light 

 one is forced to recognize that certain species have sensory per- 

 ceptions of photic stimuli quite as well defined as exist in such 

 organisms as the earthworm, clam, etc. And while in this group 

 of ccelenterates no such definite sensory organs are known as 

 those found in many medusae, the Hertwigs have described cer- 

 tain ectodermal cells which they have designated as sensory in 

 function. It is not without some warrant that we may conclude 

 that the various aspects of behavior under consideration are more 

 or less definitely correlated with sensory structures and perhaps 

 nerve cells. 



2. Loeb, who has studied certain aspects of the behavior of 

 Ceriantlins ineinbrauaceiis (" Physiology of the Brain," pp. 5659), 

 attributes them to the influence of two tropic forces, namely, 

 geotropism and heliotropism. " Positive geotropism and positive 

 stereotropism cause the Cerianthi to burrow in the sand ver- 

 tically, and positive geotropism keeps them permanently in the 

 burrow." 



I have elsewhere shown the inadequacy of this explanation as 

 applied to tube-dwelling annelids. I believe the facts under 

 review may likewise be better understood and more consistently 

 explained by other modes. Certainly the factor of light must be 

 reckoned with as potent in the behavior of the several species 

 studied. Again the variable behavior of these creatures in their 

 burrowing habits is not easily accounted for on the usual theory 

 of tropisms. Furthermore, it seems highly probable that in some 

 cases the food-taking habit may sustain a relation to the general 

 tube-dwelling habit. 



3. Finally, as one considers the interesting facts as to the distri- 

 bution of these light-reacting anemones the foregoing inferences 

 are strongly corroborated. It is not necessary to review these 

 facts in detail. It will be recalled that the observations of Quat- 

 refages and Haime, already cited, had to do with species of Cerian- 

 tlins and Edzvardsia both of burrowing habit. Those of the Hert- 

 wigs were made on a species of Cladactis, an inhabitant of the deep 

 sea. The observations of Jourdan were made on a species of 

 Paractis, whose habit is not given, though species of this genus 

 taken by the Challenger Expedition were also from the deep sea. 



