INTRODUCTION 7 



including Europe and the adjoining islands ; Africa north of 

 the Sahara ; and the whole of Asia, except the southern half 

 of Arabia and the mainly tropical parts that lie east of the 

 Indus and south of the Himalayas and Yangtsekiang. 



(2) Ethiopian Region, including Africa and Arabia south 

 of the tropic of Cancer, as well as Madagascar and the 

 adjacent small islands. 



(3) Oriental or Indian Region, including the tropical 

 parts of Asia that lie east of the Indus and south of the 

 Himalayas and Yangtsekiang, as well as the great islands of 

 Ceylon, Sumatra, Java, Borneo, and the Philippines. 



(4) Australian Region, including Australia, New Guinea, 

 Celebes, and the smaller interjacent islands, as well as New 

 Zealand and Polynesia. 



(5) Neotropical Region, including South America, Southern 

 Mexico and Central America, and the West Indies — corre- 

 sponding with Huxley's Austro-Columbian Province. 



(6) Nearctic Region, including North America north of the 

 tropic. 



III. — The Phylum Arthropoda and its Position. 



The Arthropoda are defined as animals that are composed 

 of a series of segments, and that possess jointed appendages 

 and a firm cuticle or exoskeleton. They are most nearly 

 related to the Annelida, or Segmented Worms, and have 

 even been classified in one group with them. They resemble 

 the Annelida in the segmentation of the body, in the paired 

 appendages, in the form and position of the nervous system, 

 and in the position of the heart ; but they differ from the 

 Annelida — to consider obvious superficial characters only — 

 in having the appendages segmented, in having at least 

 one pair of appendages modified to form jaws, and in having 

 a firm exoskeleton connected with an elaborate system of 

 striated muscles. There is, indeed, one small group of 

 Arthropoda — the Onychophora, of which the extraordinary 

 Peripatus is the type — in which, besides certain other striking 

 Annelidan features, the cuticle is soft and the body-wall is 

 a simple tube of unstriped muscle ; so that we have in this 

 group an undoubted link between the two phyla. 



