The British Guiana Museum. 225 
one from a pond in the Botanic Gardens ; others from 
the rivers. These are all types of a very important class 
of animals (Crustacea), some of which grow to a large 
size, while others are perfectly microscopic. They are 
characterised by having the body inclosed in a distin6l 
crust or shell, which, in the larger forms such as the crabs 
and lobsters, becomes very hard, and is shed periodically ; 
by having the body and the limbs jointed, the limbs 
around the mouth forming biting organs ; and by breath- 
ing air, dissolved in water, by means of gills. They are 
closely related to the insects, but are distinguished 
chiefly by their aquatic mode of life and mode of respira- 
tion, by the number of their limbs, and by the absence of 
wings. Different forms of these animals are represented 
on the chart of the class on the landing. 
A star-fish with its curious radiate form, and a sea- 
egg or sea-urchin (Echinus) from which the spines 
(through which it derives another common name " sea- 
hedgehog") have been broken away, are also exhibited. 
These are comparatively lowly organised animals, less 
highly organised than the crustaceans or insects. The 
alimentary, nervous, reproductive and other systems are 
of simple structure. They possess an outer covering 
that is very firm and hard, often covered with spines, 
but this test is bored along certain areas to allow very 
minute fleshy tubes to be protruded, and, by means of 
these tubes, water is taken into the interior to a system 
of vessels, and locomotion is effe6led. The star-fishes 
are capable of undergoing very great mutilation. Thus 
two, three, or even tour of their arms may be cut off and 
yet the animals survive and reproduce the lost parts. 
They possess a very capacious stomach, and being able to 
