DEPARTMENT OF MARINE BIOLOGY. 



187 



On July 25, after the sand had been swallowed for 30 days by the holo- 

 thurian, it was found that 380.5 grams had disappeared, being dissolved by 

 the acidity of the alimentary tract of the holothurian; and as the specific 

 gravity of the sand was 2.43 it appears that about 156 c.c. of sand had disap- 

 peared. Thus these animals may be quite efficient in deepening lagoons over 

 the limestone floors of which they are abundant. 



Other experiments showed that large holothurians, such as H. Jloridana, 

 at Tortugas, Florida, may defecate from 72 to 94 grams of sand (dry weight) 

 per 24 hours. Also, when full of sand, the fluid of their alimentary tract is 

 usually alkaline and about 7 Ph, but when the animal is empty the fluid usually 

 becomes quite acid, ranging from 4.75 to 7 Ph. Thus it seems that the presence 

 of limestone sand in the guts reduces the acidity of their fluid, as would be 

 expected were the sand dissolved by the acid. 



We may conclude that holothurians are a significant factor in causing lime- 

 stone to disappear from the floor of reef-flats, one holothurian, such as the 

 specimen experimented upon, destroying about 1,870 c.c, or 114 cubic inches 

 of limestone per annum. 



Death from High Temperature due to Accumulation of Acid in the Tissues, 

 by Alfred Goldsborough Mayer. 



I find that there is a converse relation between the rate of oxygen con- 

 sumption in reef corals and their ability to resist high temperature, those 

 corals which are most readily killed by heat having the highest metabolism 

 (rate of oxygen consumption). 



Also, if sea-water be supersaturated with carbon-dioxide gas, the toxic 

 effect is in the same order as that of high temperature. That is to say, those 

 corals which are readily killed by heat are also correspondingly easily killed by 

 H2CO3. 



This toxic effect of carbon dioxide is not due to its replacing some of the 

 oxygen of the sea-water, for I find that corals are remarkably insensitive to a 

 reducoion in oxygen-supply, all species except Acropora living more than 11 

 hours in sea-water, under an air-pump which reduced the oxygen to less than 

 5 per cent of that of normal sea-water; and even Acropora can withstand 6 

 hours of this treatment. 



We know, indeed, from the studies of M. Henze, that sea-anemones use less 

 oxygen the less its concentration in the sea-water, and in 1917 J. F. McClendon 

 found that the medusa Cassiopea can survive without apparent injury for 

 more than 7 hours in the absence of oxygen, and during this time does not give 

 out CO2. Thus these coelenterates can temporarily suspend their metabolism 

 for a protracted period if oxygen be absent. 



