process of evolution has been effected, to what extent it has taken place, under what conditions and laws it has been carried out, and how far it may be regarded as merely auxiliary and supplemental to some deeper law of change and progress, are questions to which, in spite of the brilliant generalisations of Darwin, no satisfactory answer can as yet be given.  In the successful solution of this problem—­if soluble with the materials available to our hands—­will lie the greatest triumph that Palaeontology can hope to attain; and there is reason to think that, thanks to the guiding-clue afforded by the genius of the author of the ‘Origin of Species,’ we are at least on the road to a sure, though it may be a far-distant, victory.

APPENDIX.

TABULAR VIEW OF THE CHIEF DIVISIONS OF THE ANIMAL KINGDOM.

(Extinct groups are marked with an asterisk.  Groups not represented at all as fossils are marked with two asterisks.)

INVERTEBRATE ANIMALS.

SUB-KINGDOM I.—­PROTOZOA.

Animal simple or compound; body composed of “sarcode,” not definitely segmented; no nervous system; and no digestive apparatus, beyond occasionally a mouth and gullet.

CLASS I. GREGARINIDAE.**
CLASS II.  RHIZOPODA.
  Order 1. Monera.**
     " 2. Amoebea.**
     " 3. Foraminifera.
     " 4. Radiolaria (Polycystines, &c.)
     " 5. Spongida (Sponges). 
CLASS III.  INFUSORIA.**

SUB-KINGDOM II.—­COELENTERATA.

Animal simple or compound; body-wall composed of two principal layers; digestive canal freely communicating with the general cavity of the body; no circulating organs, and no nervous system or a rudimentary one; mouth surrounded by tentacles, arranged, like the internal organs, in a “radiate” or star-like manner.

CLASS I. HYDROZOA.
  Sub-class 1. Hydroida ("Hydroid Zoophytes"). Ex.
   Fresh-water Polypes,** Pipe-corallines (Tubularia), Sea-Firs
   (Sertularia).
  Sub-class 2. Siphonophora** ("Oceanic Hydrozoa").
   Ex.  Portuguese Man-of-war (Physalia).
  Sub-class 3. Discophora ("Jelly-fishes").  Only known as
   fossils by impressions of their stranded carcasses.
  Sub-class 4. Lucernarida ("Sea-blubbers").  Also only
   known as fossils by impressions left in fine-grained strata.
  Sub-class 5. Graptolitidoe* ("Graptolites"). 
CLASS II.  ACTINOZOA.
  Order 1. Zoantharia. Ex.  Sea-anemones**
             (Actinidoe), Star-corals (Astroeidoe).
  Order 2. Alcyonaria. Ex.  Sea-pens
             (Pennatula), Organ-pipe Coral (Tubipora),
             Red Coral (Corallium).
  Order 3. Rugosa ("Rugose Corals").
     " 4. Ctenophora.** Ex.  Venus’s Girdle (Cestum).