360 What are Animals and Plants ? 



species that they probably equal in the number of their 

 kinds the whole mass of beasts, birds, and reptiles taken 

 together ! 



But such creatures as these form but a very small pro- 

 portion of all animals. Creatures such as snails and oysters 

 form another vast group, known as ' mollusks.' 



Worms, also, have been formed into a division, so varied 

 in nature and so prodigious in number that their proper 

 classification is amongst the most difficult of zoological 

 problems. 



The star-fishes and their allies constitute another great 

 group, rich both in species and diversities of form. 



But the whole of the creatures we have yet referred to, 

 taken together in one mass, are far exceeded in the number 

 of their distinct species by the class of insects alone (of which 

 one or more are associated with the life of each and every land 

 plant, and probably that of every higher animal also) ; while 

 closely allied to insects are the multitudinous tribes of 

 lobsters, shrimps, crabs, spiders, and scorpions. 



We have also to take into account those coral animals 

 which have actually built up large tracts of the earth's 

 habitable surface ; and besides these, we have their humble 

 followers, the sponges. 



All the creatures yet referred to are cognisable by our 

 ordinary senses; but there are, as is commonly known, 

 myriads of kinds, either so small as to be altogether invisible 

 to the naked eye, or elsa invisible as regards the main points 

 of their structure without the aid of the microscope. All the 

 lowest animals, the bodies of which are not made up of dis- 

 tinct organic substances, or tissues, are called Protozoa. 



Then, as to plants : besides the families of flowering trees, 

 shrubs, creepers, and herbs, with members of which we un- 

 consciously become more or less familiar, there are a multitude 

 of other families, specimens of which we only see in our 



