130 



The hish Aattiralist. 



July, 



each gathering, higli and low water, care being taken to pit 

 against the high-level groups, low-level groups as closel}' as 

 possible in the same stage of maturity. The results as set 

 out in the following table place beyond doubt the greater 

 vitality or adaptability of the high-level individuals at all 

 stages from the fourth to the eighth day of exposure. 



TablK shewing the comparative vitality on exposure to air in a dry room 

 oi Parpura lapillus gathered {ii) at or above high-watermark and (/;) 

 at low-water mark. 



The figures in the last column of this table are much too 

 high, as by inadvertence the 8-days groups were allowed for 

 revival in sea water twice as long a period, i.e. 24 hours, as the 

 preceding groups. The efi'ect was necessarily to yield a 

 disproportionate number of survivals or resuscitations, so that 

 the fairly regular decline of vitality was interrupted by a 

 sudden jump upwards. The results above tabulated might 

 also have been exhibited in descending and diverging curves 

 or slopes passing from full vitality to total extinction, but in 

 that form would have been less easily grasped. 



With the second species, L. rudis, no such detailed obser- 

 vations were made, but such as were carried out gave similar 

 results. On two occasions small groups of high-water and 

 half-tide specimens of this species were pitted against each 

 other. On the first occasion all the individuals had been ex- 

 posed in air for 2\\ days, on the second for 22^ days, A 12 

 hours' immersion in sea water of each of the four groups or 

 batches restored to full vitality 80 per cent, of the high-water 

 groups to but 40 per cent, of the half-tide groups. In com- 

 parative tolerance of fresh water and water of treble the salinity 

 of sea water both species yielded results in full accordance 

 with expectation, as will appear from the following table : — 



