INTRODUCTION. I I 



Mivart, in his introductory pages to The Common Frog, 

 (1874), gives seven great groups, " each of which is characterised 

 and defined by certain points of structure possessed by the 

 animals which compose it, and which serve to distinguish them." 



1. Annulosa. — With bodies composed of a series of segments or rings, 



placed one behind the other, as in earth-worms, centipedes, wood- 

 lice, all insects, lobsters, crabs, scorpions, spiders, and leeches. 



2. Mollusca. — Snails, slugs, cuttle-fish, and shell-fish. 



3. Molluscoid.b. — Sea-squirts or Ascidians (sometimes called Ttinicates), 



and lamp shells, together with minute aquatic animals in compound 

 aggregations. 



4. Annuloid/e. — Star-fishes, sea-urchins, together with internal parasites 



(tape-worms, etc.), and their allies. 



5. Coelenterata. — Sea anemones, jelly-fish, polypes, and the coral 



animals. 



6. Protozoa. — Sponges, the Infusoria, and all the lower forms of animal 



life. 



7. Vertebrata. 



Dr. Henry Alley ne Nicholson, in his popular Manual of 

 Zoology (1878), gives six types or plans of structure, technically 

 known as " Sub-kingdoms," viz. — 



1. Protozoa; 2. Ccelenterata ; 3. Annuloid^e ; 4. Annu- 

 losa ; 5. Mollusca ; 6. Vertebrata. 



CasselFs Natural History (1881), edited by Prof. Martin 

 Duncan, is also a popular work. His sub-divisions of the Inver- 

 tebrata are six, differing somewhat from those given above, viz. — 



1. Mollusca; 2. Arthropoda; 3. Vermes; 4. Echixo- 

 dermata ; 5. Zoophyta; 6. Protozoa; with two 

 intermediate groups, Molluscoid^e and Tunicata. 



There has lately (1884) been translated into English an important 

 work, The Text-Book of Zoology, by C. Claus, of the University 

 of Vienna. He says : — " In the present state of science we 

 consider it convenient to distinguish nine types as the chief 

 divisions, and to characterise them as follows, — 



1. Protozoa. — Minute, and without cellular organs. 



2. Ccelenterata. — Radiate animals segmented into 2, 4, or 6, with a 



central body cavity. 



