66 N. Annandale : The FaiDia of Brackish Ponds. [Yol.. I, 



The pond race of the Actinian is not subject to the same 

 periodical exposure as the t^'pical form of the species, for under 

 ordinary conditions it Hves bej'ond the reach of the tides. It is, how- 

 ever, exposed to gradual changes in the salinity of the water to which 

 it is restricted. To what extent it is able to survive such vicissi- 

 tudes is still uncertain ^ ; if Stoliczka is right as regards the chitinous 

 nature of the membrane which covers the egg of the typical form, 

 and if the egg of the pond race has a similar covering, the egg is 

 well fitted to withstand chemical changes in the environment, and 

 even desiccation. Adults of the pond race are able to live for 

 some hours lying on the ground exposed to the sun. Under such 

 conditions their behaviour is totally different from that of ex- 

 amples of the typical form. I have found individuals of moderate 

 size lying on the mud at the edge of a tank. Their tentacles were 

 completely retracted and the sphincter was tightly closed ; their 

 columns were, however, distended with water, which was contained 

 in the coelenteron. 



Under natural conditions both forms of the species are diurnal 

 in habit, the typical form remaining with its disk fully expanded 

 when exposed to the direct rays of the sun. The new race, however, 

 is usually found below or among floating algse according to its age, 

 and these provide considerable shade. Young and half-grown in- 

 cHviduals in my aquarium became practicall}' nocturnal after a few 

 days' exposure to bright light in a glass vessel. At night and early 

 in the morning they expanded their tentacles, which were withdrawn 

 as soon as the day became warm (c/. Fleure and Walton (12), 

 p. 217). Individuals of the typical form living under identical con- 

 ditions exhibited a similar tendency, but to a less marked degree ; 

 full-grown examples of the race never lived for at most more than 

 three days in these conditions. Young examples of this form showed 

 less power of resistance to the unnatural conditions of a small 

 aquarium than did adults of the typical form, the latter living 

 for over three months in water which was always kept ol the same 

 salinity, while those from the pools, in the same vessel, as a rule died 

 in about a fortnight. The water in which they were, was taken 

 from one of the ponds at Port Canning and was brought to Calcutta 

 in a stoppered bottle. 



Movements. — 



Notwithstanding what appears to be an avoidance of bright 

 light in the case of the variety, neither form of the species exhibits 

 any marked heliotropism, negative or positive, in its movements. 

 When individuals are placed in a glass vessel lighted from one side, 

 they remain, other conditions being suitable, where they are placed, 

 neither moving towards the light nor away from it. Stoliczka 

 noticed, however, that his specimens showed a tendency to move 

 upwards towards the surface of the water, and I find that mine prefer 



1 Almost at the end of the hot weather, the Artinian is still abundant in the ponds. 

 May 27th, 1907. 



