on the motions of Infusoria. 3 47 



ing perceptibly influenced by that agent. Actinice placed 

 alive in basons of sea water I have observed to move slowly 

 along the sides of the vessels till they reached the most shaded 

 situation, where they generally remained stationary, and they 

 appear to shun the light in their native element. I have often 

 verified the observations of Trembley on the fondness of the 

 Hydroe for light. When placed in a glass jar with pure wa- 

 ter, they quickly betake themselves to the illuminated side of 

 the vessel, and collect in that situation. In their natural abode 

 they show their partiality to light by approaching to the sur- 

 face of the water, where they are generally found adhering to 

 the stalks of floating Lemnce. When we watch the motions of 

 Meduscc floating in the sea, we generally observe them change 

 their direction as they approach the surface, and direct their 

 course downward before any part of their body has come into 

 contact with the atmosphere. From seeing this often take 

 place where the water was quite still, I have been induced to 

 believe that the delicate transparent texture of the animal was 

 sensible to the blaze of the sun's light as it approached the 

 surface. I have elsewhere remarked that even the ova of some 

 zoophytes preferred to attach themselves to the shaded parts 

 of the vessels in which they were placed. From the soft ge- 

 latinous texture of such beings, indeed, it seems natural to ex- 

 pect that an agent impinging on them with such velocity and 

 in so great a quantity as the rays of light, and which pene- 

 trates their whole substance, should be able to affect them in 

 some manner, were it only with impressions of touch. And 

 the examination of the localities and the particular positions 

 habitually assumed by the lowest species of fixed and nerveless 

 animals, where the temperature and pressure do not vary, lead 

 us to conclude that their physical distribution is principally 

 determined by the intensity of light. 



From the minuteness of the Infusoria and their transparent 

 colourless texture, and also from the manner in which they are 

 generally examined, in watch-glasses under the microscope, 

 the influence of light on their motions has probably escaped 

 notice. The motions are most easily observed in those which 

 have a perceptible magnitude with some degree of opacity and 

 a lively colour, as the Furcocerca viridis of Lam. (Cercaria 



