10 THE STUDY OF ANIMAL LIFE CHAP. 



Worms " form a vast, heterogeneous " mob," heart- 

 breaking to those who love order. No zoologist ever 

 speaks of them now as a " class " ; the title includes many 

 classes, bristly sea-worms and the familiar earthworms, 

 smooth suctorial leeches, ribbon-worms or Nemerteans, 

 cylindrical thread-worms or Nematodes, flat tapeworms 

 and flukes, and many others with hardly any characters 

 in common. These many kinds of " worms " are full of 

 interest, for in the past they must have been rich in pro- 

 gress, and zoologists find among them the bases of the 

 other great branches Vertebrates, Molluscs, Arthropods, 

 and Echinoderms. Worms ' lie (as it were) in a 

 central pool, from which flow many streams. 



Lower still, and in marked contrast to the rest, are 

 the Stinging-animals, such as jellyfish throbbing in the 

 tide, zoophytes clustering like plants on the rocks, sea- 

 anemones like bright flowers, corals half-smothered with 

 lime. The Sponges are the lowest animals with " bodies." 

 They form a branch of the tree of life which has many 

 beautiful leaves, but has never risen far. 



Beyond this our unaided eyes will hardly lead us, yet 

 the pond- water held between us and the light shows 

 vague specks like living motes, the firstlings of life, the 

 simplest animals or Protozoa, almost all of which have 

 remained mere unit specks of living matter, with com- 

 plexities indeed, but at a microscopically minute level. 



It is easy to write this catalogue of the chief forms of 

 life, and yet easier to read it : to have the tree of life as 

 a living picture is an achievement. It is worth while to 

 think and dream over a bird's-eye view of the animal 

 kingdom to secure representative specimens, to arrange 

 them in a suitably shelved cupboard, so that the out- 

 lines of the picture may become clear in the mind. The 

 arrangement of animals on a genealogical or pedigree 

 tree may be readily abused, but it has its value in pre- 

 senting a vivid image of the organic unity of the animal 

 kingdom. 



If the catalogue be thus realised, if the foliage come to 

 represent animals actually known, and if an attempt be 

 made to learn the exact nature, limits, and meaning of 



