Marvels of the Universe Ite 
much in the same way as a dog uses his 
tongue, for, it seems impossible it can abso- 
lutely absorb nourishment in the way that the 
proboscis of the blow-fly does, for example, 
seeing that there is an entire absence of any 
arrangement for so doing. 
A LIMESTONE COMPOSED OF 
WATER-FLEAS 
BY F. CHAPMAN, A.L.S., F.R.M.S. 
In our ponds and runnels swarms of tiny bi- 
valved crustaceans are always to be found. 
These are known as Water-fleas (see page 408). 
They are sometimes so numerous as to form 
thick beds of sediment as they die and fall to : : 
the bottom with the mud. The organic matter ” Photo by] ; ; 7 [F. Chapman. 
of their bodies not infrequently gives rise to ER DO EIMESTONE. 
awe Z ; A thin section of this Limestone from Dorset, as seen under 
quantities of petroleum, which remains locked the microscope, showing the shells of ancient Water-fleas of 
up in the shales of certain formations like the “ch it is made up. 
Carboniferous of Scotland. Some of the limestones of the Isle of Purbeck are mainly composed of 
the little valves of these lowly crustaceans. The genus to which they belong is now extinct, but 
we know from the accompanying mussel-shells, turtle-bones and the remains of crocodiles that the 
prevalent conditions were of the nature of fresh-water lakes and brackish or estuarine river-mouths 
and swamps bordering the sea of the Jurassic period. The accompanying photographs show a 
magnified view of the weathered surface of a 
piece of limestone, and a thin section of the 
same, from Swanage Bay, Dorsetshire. 
CADDIS-CASES 
In clear-water ponds and shallow streams, one 
may see from the bank a number of more or 
less cylindrical objects moving over the bottom. 
These cylinders are variously composed accord- 
ing to the situation where they are found. 
Some are constructed of grains of sand 
cemented together, others of small fragments 
of gravel, cut leaves, short lengths of twigs, 
small bivalve shells, snail shells, and so forth. 
They are well-known to every rural schoolboy 
as Caddis-cases, and to have been constructed 
as a protection by a tender-bodied grub. In 
the course of time this grub becomes a chrysalis, 
and later emerges as a four-winged Caddis-fly. 
There are many species of Caddis-fly, and 
a naturalist who has studied the group can “7” a , TRC 
tell by the Caddis-case to which species the CYPRID LIMESTONE. 
contained grub belongs. Each kind has its The weathered surface of the Limestone is seen more highly 
magnified, and exhibits the general form of the fossil Water- 
own special taste in the matter of building fleas more clearly, 
$4 
