ANIMAL CLASSIFICATION 25 



somewhat the brief outline of the past history of the 

 animal kingdom, which has already been given. Since 

 the appearance of the Origin of Species, the zoologist, in 

 making his classifications, has attempted as far as possible 

 to set forth a genealogical arrangement. Our purpose 

 will be served by an account of the main outlines of 

 a recent classification, which has been framed with a due 

 consideration for all sides of zoological research, new 

 and old, and has met with general approval. Professor 

 Lankester divides the animal kingdom into two Grades, 

 the higher of which, the Enterozoa (Metazoa), were 

 derived from the lower, the Plastidozoa (Protozoa). Each 

 of these grades is again divided into two sub-grades, and 

 each of these is again divided into Phyla, corresponding 

 more or less to the older Sub-Kingdoms. Beginning 

 from below, the most primitive animals in existence are 

 found in the seven Phyla of the lower Protozoan sub- 

 grade, the Gymnomyxa. Of these unfortunately only 

 two, the Reticularia (Foraminifera) and Radiolaria, 

 possess a structure which renders possible their preserva- 

 tion in the rocks. The lowest and simplest of these 

 Gymnomyxa represent the starting-point of that scheme 

 of organic evolution which we are considering to-day. 

 The higher order of Protozoan life, the sub-grade Corti- 

 cata, contains three Phyla, no one of which is available in 

 the fossil state. They are, however, of great interest 

 and importance to us as showing that the Protozoan type 

 assumes a far higher organization on its way to evolve 

 the more advanced grade of animal life. The first-formed 

 of these latter are contained in the two Phyla of the sub- 

 grade Coelentera, the Porifera or Sponges, and the 

 Nematophora or Corals, Sea- Anemones, Hydrozoa and 

 allied groups. Both of these Phyla are plentifully repre- 

 sented in the fossil state. It is considered certain that 

 the latter of these, the Nematophora, gave rise to the 

 higher sub-grade, the Coelomata, or animals with a coelom 

 or body-cavity surrounding the digestive tract. This 

 latter includes all the remaining species of animals in nine 

 Phyla, five of which are found fossil — the Echinoderma, 

 Gephyrea, Mollusca, Appendiculata, and Vertebrata. 



