214 THE SCIENCE OF LIFE. 



opment. In many respects Myriapods are like Worms, 

 yet their heads show a resemblance to Insects. Some 

 Spiders are less complicate than Myriapods, yet for their 

 wonderful instincts Owen places them above Insects. 

 Insects begin life as worm-like embryos. Classes in the 

 articulate type depend on the equal or unequal develop- 

 ment of the body-segments, and the number and form 

 of appendages. Articulates with jointed appendages 

 articulated to the body are called Arthropoda, (Gr., art/i- 

 ron, a joint ; podes, feet.) 



2. The class of WORMS, called, also, Annelida, or An- 

 nulata, (Annulus, a little ring,) includes animals with a 

 soft skin and a body formed of a succession of rings, or 

 movable joints. They differ from the Anthropoda in 

 not having jointed limbs. A water-vascular system ex- 

 ists, but it has no connection with locomotion. The 

 blood is often reddish, but the color does not depend on 

 colored corpuscles, as in vertebrates. The circulatory 

 apparatus is more highly developed than in Insects. 



Some worms can only live as parasites upon the blood 

 or juices of other animals, and in these the circulatory, 

 water-vascular, and digestive systems become rudiment- 

 al, the nervous system is undeveloped, the body-cavity 

 often vanishes, and the reproductive organs alone are 

 fully represented. 



Order i. Tceniada ; (tcenia, a tape.) Tape-worms, so 

 called from their length and flatness. They live chiefly 

 in the digestive canal of higher animals. Three species 

 are occasionally parasitic in man. The head, which is 

 the true animal, is provided with hooks or suckers, by 

 which it adheres to the mucous membrane of its host. 



