i] THE HABITAT OF CONVOLUTA 21 



posed now to the violence of the sea and now to the 

 hot sun striking on the drying, emerged rocks and 

 weeds, C. paradoxa has chosen its abiding place. But, 

 unlike C. roscoffensis, C. paradoxa fails to finds in its 

 station a regular recurrence of change, and hence it 

 is constrained to shift its station during the lunar 

 periods. At times of slack tide, the seaward part of 

 the C. paradoxa zone is submerged continuously and 

 the light which reaches the animals clinging to weed 

 some feet below the surface is too feeble for their 

 requirements. Hence, during such tides, C. paradoxa 

 edges up landwards to the shallower water and reaches 

 so far as the Fucus zone. During the spring tides, this 

 latter zone is left high and dry for hours and hapless 

 C. paradoxa stranded there would suffer from the 

 intense isolation and also run the risk of desiccation. 

 So, as the tides increase, it works its way down the 

 beach, reaching, at the median spring tides, to the 

 more seaward weeds, and at the largest springs, when 

 these weeds may no longer harbour it in submerged 

 peace, it treks again yet further toward the sea and 

 takes up its station among the tangle of fine weeds 

 which hang in tassels from the finger-like, dark brown 

 Pycnophycus. During the slack periods, at low water, 

 when the landward part of the Pycnophycus zone is 

 uncovered, C. paradoxa creeps into the deepest re- 

 cesses of the matted, emerged weeds. Soon, the 

 making tide covers the Pycnophycus with an in- 



