INSECTS. 



139 



Fig. 246. — Tunicate. 



TUNICATES. 



These animals have no shell, but 

 are covered with a tough tunic, or 

 skin. Sometimes they grow in clus- 

 ters, attached by a stem to seaweed, 

 rocks, or floating timber. They 

 var)' from the size of a pea to several 

 inches in diameter. They are some- 

 times called Ascidians, from a word 

 which means a leather bag. Strange 

 as it may appear they are not distantly related to the 

 Vertebrates, as is shown by their development. 



ARTHROPODS, OR JOINTED ANIMALS. 



Arthropods have no internal skeleton ; the hard 

 parts are exterior; the body is made up of a series of 

 similar rings, each of which bears a pair of jointed legs. 

 They include the Insects, — Bees, Butterflies, Flies, 

 Beetles, Bugs, Grasshoppers, Darning Needles, etc., — 

 Spiders, Scorpions, Mites, Lobsters, and Shrimps. 



INSECTS. 



Insects breathe by means of air holes along the sides 

 of the body, the openings of branching air tubes which 

 carry air to every part. The term Insect means citt 

 into; the animals seem to be cut into, or jointed. The 

 body is divided into three parts, — the head, middle 

 body or thorax, and hind body or abdomen. On the 

 head and near the eyes are two jointed members, called 

 antenna;, supposed to be connected with the sense of 



