THE TASMANIAN NATURALIST. 
7 1 
another, but in the lower microscopical groups there is often some 
•difficulty in deciding whether certain small creatures are plants or animals. 
Roth of these great kingdoms can be divided up into lesser groups 
and in the case of animals, some are distinguished by the fact that they 
possess a particular part of the skeleton known as the backbone or 
vertebral column, which is made up of a number of bones joined together 
in such a way as to form a firm but flexible axis. Such an animal 
possessing a backbone is called a vertebrate or backboned animal. 
Animals which do not posses a backbone at any time either when young 
•or grown up are called invertebrate animals. Of the kingdom Animalia 
•(animals) then, we have two large divisions or sub-kingdoms the 
Vertebrate and the Invertebrate . 
We have, now, in a brief space, to deal with the main groups of 
invertebrate animals. When we come to look at these animals as a 
whole, we find that they can be gathered together into various large 
groups, e.g., all animals which have rings running round their bodies 
(worms) can be brought together into a group by themselves, and these 
•called Annulata (ringed) Again, there is an enormous number of 
animals which among other things, resemble one another in the possess¬ 
ion of long, many-jointed legs. Such animals are crabs, crayfishes, 
lobsters, insects, spiders, centipedes, scorpions, &c., and these are in¬ 
cluded in the group known as Arthropoda (animals with jointed feet, 
Uk. arthros a joint, pos. a foot). Each of these large groups is called a 
phylum (pi. phyla). 
The lowest phylum of invertebrate animals is the Phylum Protozoa , 
•every animal in which consists of a single small portion of a substance 
•called protoplasm in which is a small central condensed portion, the 
nucleus. Such a portion of protoplasm with a nucleus is called a cell, 
and the phylum Protozoa consists of animals which are made up of 
•one cell or are unicellular. All the other phyla consist of animals made 
•up of many cells (multicellular). 
Pig. 1 Fig. 2 
Pig i. — Atn&ba. A unicellular aninuil, consisting of an irregular piece of protoplasm 
with a nucleus (».) 
Pig 2. — A sponge (Sycon). At the ends of the cylinders are the apertures (o) by means 
of which the water leaves. 
