2 PRIMARY DIVISIONS OF THE ANIMAL KINGDOM. 



their connectives, forming the oesophageal ring, whence proceed 

 the principal cephalic nerves. Reproduction is oviparous usually, 

 sometimes ovoviviparous. 



In the Brachiopoda, the Tunicata and the Bryozoa the nervous 

 system is more simple. These animals have usually been con- 

 sidered mollusks, but the two latter are now definitely excluded 

 from the mollusca proper, whilst the former, despite structural 

 and physiological affinities with the others, still receives the 

 attention of Conchologists, mainly on account of its protecting 

 bivalve shell. They together constitute a subdivision Mollus- 

 coida. 



III. Articulata. Crabs, spiders and insects. The outer 

 integument of the body is horny, composed of segments, bearing 

 articulated locomotive members. The nervous system consists 

 of pairs of ganglia arranged in the middle line of the body. 



IV, Vermes. The body of worms is composed of segments, 

 sometimes bearing non-articulated appendages. The nervous 

 system varies ; in the worms proper it is as complicated and 

 similarly arranged to that of the articulates ; in other forms it 

 is reduced to a simpler structure. The digestive canal also 

 varies : it has two orifices in the worms proper, the anus is 

 wanting in the Planarians, and in the Cestoides and Acantho- 

 cephala there is no specialized alimentary tube. 



y. Echinodermata. Star-fishes, sea-urchins, etc., sometimes 

 called Radiata from their radiated structure. The animal is pro- 

 tected by an external shell or covering, sometimes calcareous. 

 ■ The nervous system consists of several trunks, which unite to 

 form a ring around the mouth. The digestive tube is distinct 

 from the visceral cavity : there is also a closed circulatory 

 system. 



YI. Gcelenterata. Coral animals. Actiniae, Hydra, etc. In 

 these the digestive apparatus is not specialized as in the Echino- 

 derms but communicates or is confounded with the general 

 cavity of the body. There is no closed circulatory system, and 

 no nervous system has been detected except in some of the 

 medusae, where it is quite rudimentary. 



VII. Spongifera or Porifera. The body-cavity is lined with 

 vibratile cilia, which aid in expelling through its orifice the 

 digestive products and eggs ; this central cavity communicates 

 through a system of afferent canals with the exterior, their outer 

 openings representing multiple mouths. 



VIII. Protozoa. Microscopic gelatinous animalcules, appar- 

 ently without distinctive organs. 



The above classification is modified from a well-known one of 

 Prof. Huxley (though not his latest effort in this direction), and 

 in the first subkingdoms agrees with the more ancient system of 

 Cuvier. It is principally the Radiata of the distinguished 



