672 
Analyses of Books. 
[November, 
rest. All animal and vegetable matter which is in a suitable 
condition is digested and assimilated, whilst the residue, very 
finely divided, is ejedted in the form of little globular pellets. 
With this matter they line the walls of their burrows, but much 
of it they bring to the surface. The weight of each casting is 
not very great ; but in order to estimate rightly what worms can 
do, we must, following Mr. Darwin, consider their number per 
acre, and form an idea of their work over a long series of years. 
Prof. Hensen, in a treatise on the habits of worms, calculates, 
from the number which he found in a measured plot of land, 
that there must be upwards of 53,000 worms per acre, or, taking 
their average weight at 15 grains each, about 356 lbs. Mr. 
Darwin found in a single cake of earth, of the size of two open 
hands, seven worm-burrows, of the diameter of goose-quills. 
A gentleman, mentioned by Mr. Dancer in the “ Proceedings 
of the Manchester Philosophical Society,” having upset some 
barrels of sour ale on his land, was amazed at the heaps of 
worms which lay dead on the surface. We have often noticed 
the multitudes of worms which fall into small water-courses cut 
in grass-lands for irrigatory purposes. If we also remember to 
what extent they are devoured by moles, birds, hedgehogs, slugs, 
and other enemies, without growing scarce, we must admit that 
their numbers are very great. The weight of the castings found 
at the mouth of each burrow varies greatly. In the case of our 
common British worm it is found, by adlual collection and 
weighing, to range from f oz. to close upon 4 ozs. But the 
author is prepared to give more exact data. A lady friend under- 
took to collect and preserve for a whole year the total worm- 
casts thrown up on two separate square yards of ground, near 
Leith Hill, Surrey. From one of the plots — a place unfavourable 
for the life of worms — the year’s castings, when dry, weighed 
3^- lbs. The other plot gave 7^ lbs. The former consequently 
would show 7^ tons of dry earth per acre, raised to the surface 
by the activity of worms, whilst in the latter it would reach 
16 tons. At the latter rate the deposit, if uniformly spread over 
the surface of an acre, would measure in the course of a single 
year 0*1429 inch, or in round numbers nearly inches. This 
quantity is somewhat smaller than the rate at which mould accu- 
mulates over objects left on the surface of the ground in a similar 
time. But Mr. Darwin points out that earth is also raised to the 
surface by moles, ants, dung-beetles, &c., and that a part of the 
worm-castings is blown away in dry weather, and washed down 
in time of rain. Thus we see that in the course of years every 
particle of the upper soil of a field or garden must have been 
finely comminuted and passed through the intestines of worms. 
It is doubtful whether their burrows contribute much to the 
drainage of the land, as worms generally stop up the opening 
with leaves, or in default with small stones. But that they admit 
air, and thus aid in the chemical changes going on in the sub- 
