116 
Prof. Ehrenberg on Microscopic Life 
where there is a complete absence of all life. In like manner the 
development of organised beings has been conceived to diminish 
from the equator to the arctic regions of the earth, the latter 
becoming first destitute of trees, then of grass, lastly of lichens 
and algce, until at the poles ice and death hold solemn reign. 
The greatest depths in the ocean at which Mollusca had been 
found to exist were, according to the observations of Mr. Cuming 
in the year 1834, the genera Venus, Cytherea, and Venericardia. 
at 50, Byssoarca at 75, and Terebratula in 90 fathom water. 
According to Milne-Edwards and Elie de Beaumont, 244 metres, 
or 732 feet, formed the extreme range for the growth of corals 
and the development of organic matter in the sea off the coast of 
Barbary. From 100 fathoms depth, Pferon drew up in the year 
1800, off New Holland, Sertularia and a variety of corallines, 
which were all luminous, and on an average three degrees higher 
in temperature than the surface of the sea. In 1824 and 1825 
Quoy and Gimard, in their valuable researches upon the struc¬ 
ture of corals, asserted that branched corallines could occur only 
in a depth of from 40 to 50 fathoms, and that in a 100 fathoms 
of water Retepora alone existed. According to Ellis and Mylius 
who wrote in 1753, the greatest known depth from which a living 
animal had been taken was the Umbellaria Encrinus, which was 
fished up by Captain Adrian, in Greenland, from 236 fathoms of 
water, equal to a depth of 1416 feet. Specimens, however, of the 
sea-bottom have been drawn up from still greater depths ; for at 
Gibraltar, Captain Smith found in 950 fathoms, or 5700 feet of 
water, sand containing fragments of shells; and Captain Vidal 
according to Mr. Lyell, detected in the mud of Galway Fi rt q, 
from a depth of 240 fathoms, only some Dentalia, the remainder 
of the sea-bottom from the same depth consisting of pulverised 
shells and other organic remains devoid of life. 
According to the calculations of Parrot, a column of sea-water 
at a depth of 1500 teet exercises a pressure of 750 pounds, or 
7.J hundred weight, upon the square inch ; and since the at¬ 
mospheric air inclosed in these animals of a delicate cellular 
structure descending from the surface of the ocean would pro¬ 
duce alternately such extremes of expansion and contraction as to 
