1 6 WORMS. 



The scholars are now sufficiently familiar with the 

 structure of the worm to understand Fig. 5, which is 

 merely a diagram representing the segmented body of 

 the worm, and the relative position of the different 

 systems : cs is the circulatory system, ds the digestive 

 system, and tis the nervous system. 



They will be able to appreciate, moreover, that what 

 is meant by a segment or ring, is an imaginary trans- 

 verse thick slice through the body, which contains in 

 itself, and carries, on its exterior, the typical organs and 

 appendages of the worm, each ring in the body being, 

 to some extent, a repetition of its neighbor. 



They will also be able to understand that the paddles 

 are true appendages formed by the budding out of the 

 walls of the body. This distinction is essential because 

 it is necessary, in comparing the Crustacea with the 

 Worms, to contrast the hard, jointed appendages of the 

 former, with the soft, unjointed paddles of the worm. 

 These appendages can not be compared with the setae 

 of the earthworm, as it has already been seen that the 

 latter are not true appendages, but simply bristles 

 adapted for locomotive purposes. 



It is well to note, however, that in having segmented 

 or jointed appendages the Lobsters differ from the Worms, 

 as do also the Mviiapods, Spiders, and Insects. In fact, 

 these types and the Crustacea can be spoken of together 

 under one name, as the Arthropoda, or animals with seg- 

 mented appendages, and thus contrasted with the Worms. 



