Si6 MANUAL OF ELEMENTARY ZOOLOGY 



ternal air tubes, with one pair of antennae, 

 numerous pairs of legs, and no wings. 

 Centipedes and Millipedes. 

 ^ d. Class Arachnida. 



For the most part land Arthropoda without 

 gills, but with internal air spaces ; and all 

 ^ without antennas and with four pairs of legs, 



i. Order Scorpionida. 



Arachnida with segmented abdomen, bearing 

 a poison sting in the telson, chelate 

 ^ pedipalpi, lung-books, and no spinnerets. 



Scorpions, 

 ii. Order Araneida. 



Arachnida with unsegmented abdomen, 

 poison glands in the cheliceras, pedipalpi 

 \s not chelate, lung-books and spinnerets. 



e.g. Epeira, Tegenaria (the House Spider), 

 iii. Order Acarina. 



Arachnida with unsegmented abdomen, 

 pedipalpi not chelate, and no lung-books 

 or spinnerets. 

 » e.g. Demodex, Sarcoptes, Ixodes. 



£. Phylum Nematoda. 



Bilaterally segmentrical, unsegmented Triplo- 

 blastica, with a spacious haemoccelic body 

 cavity, a stout cuticle, and no limbs, 

 e.g. Anguillula, Tylenchus, 'Filaria, 

 Trichinella, Ascaris, Trichocephalus, 

 Oxyuris, etc. 

 5. Phylum Mollusca. 



Bilaterally symmetrical, unsegmented Triplo- 



blastica with an open blood-vascular 



system, a perivisceral coelom of moderate 



size, a nervous system which encircles the 



forepart of the gut, a shell, but no cuticle, 



a mantle fold, and a ventral, muscular foot. 



e.g. Anodonta. Snails and Cuttlefish 



also belong to this phylum. 



^ 6. Phylum Echinodermata. 



Radially symmetrical, marine Triplpblastica 

 without true blood vessels, with a spacious, 





