^Q Part second. 



The animals of the Mediterranean are so accustomed to such 

 long-estabHshed narrow temperature hmits that they suffer as soon 

 as these are exceeded. Even an approach to the hmits is often 

 harmful and many animals protect themselves by burrowing in 

 the sand, as for instance does the spider-crab, Maja (fig. 70) in 

 summer and the fish Coris (fig. 157) in winter. The summer and 

 winter extremes of temperature produce in many of the sessile 

 animals (Hydroids, Corals, compound Ascidians, Bryozoa) ex- 

 traordinary phenomena which are also caused by other conditions 

 harmful to the organisms. These changes must also be looked 

 upon as means of protection. The animal assumes the appearance 

 of death, while some of the functions of life are set aside — are 

 so to speak "latent" — in order the better to withstand the un- 

 favourable conditions. The reader has doubtless, in this connec- 

 tion, already called to mind the winter sleep of the marmot, but 

 in the case of the Hydroids and Corals life is much more latent. 

 This state changes them into mere skeleton, nothing living being 

 visible from the outside. The living substance is resting within, 

 however, rolled up to a structureless mass at the base of the 

 skeleton and this will fully regain its formative power on the 

 return of favourable temperature conditions. But only few 

 animals possess such contrivances for protecting themselves and 

 if we restricted ourselves to them, the tanks of the Aquarium 

 would be very deserted. In summer it is indeed possible to keep 

 the temperature of the water in the Aquarium below the maximum 

 of that in the Bay, by means of increased pumping and shortening 

 of the nightly pauses, and seldom has it risen above 24 ^ C. But 

 even this is too much for many animals. Against the cold, how- 

 ever, continuous pumping does not help and we have at present 

 no means of preventing the water from sinking below 13" C, or 

 sometimes as far down as 8® C, for weeks on end in cold winters 

 (experiments are at present being made with warm tubes). Such 

 winters are injurious to the health of even old inhabitants of the 

 Aquarium — thus in the winter of 1905 a dozen Sea-Perch which 

 had been for ten years in tank 10 were sacrificed. 



