SPECIAL PROBLEMS OF SHORE LIFE 83 



on the effects of salinity in relation to Copepoda. He has 

 found that the green weed Enteromorpha intestinalis ^ which 

 covers the pools above high-water mark, harbours enormous 

 quantities of Copepoda belonging to the genus Harpacticus. 

 The condition of some of the pools suggested that these 

 animals would probably be able to stand considerable 

 variations in the salinity of the water, as in wet weather they 

 are flooded with rain while in dry summers the pools become 

 almost or completely dried up. 



Herdman took sample tubes containing Enteromorpha 

 and Harpacticus and added fresh water until there were 

 19 parts of fresh water to i part of original sea-water. The 

 Enteromorpha appeared healthy and the Copepods had 

 increased greatly in numbers and were very active. The 

 young ones hatched in the nearly fresh water were all 

 colourless, but the adults had not lost their original bright 

 red tint. 



A second sample tube containing Enteromorpha and 

 Harpacticus, and sea- water from the pool, was emptied into 

 a shallow glass and allowed to evaporate slowly. The 

 Copepods did not increase in numbers, but they did not die 

 until the dish was almost dry and the salt had crystallised 

 out round the edges. After evaporation had been going 

 on for a few days the Copepods had retreated into the interior 

 of the Enteromorpha filaments. Possibly under natural con- 

 ditions they escape death in this way when pools have 

 dried up. 



Similar powers of resistance are possessed by Entomo- 

 straca from salt marshes, where the density of the water is 

 even more variable than in rock pools. We have, for 

 example, the classic experiments of Schmankewitsch on the 

 Phyllopod Artemia salina. According to Feronniere, Artemia 

 salina resists a density as great as i"i6 in the salt marshes 

 of Lorraine, and according to Artom (quoted by Issel, op. 

 cit.) up to I '23 in those of Cagliari. Caiman, even, has found 

 in a variety of grey salt consumed in this country, mixed with 

 the salt crystals, numerous eggs of Artemia, which in water 

 of suitable salinity are capable of developing in normal fashion. 



