

120 



ANIMAL KINGDOM. 



168, another Crustacean, having a shell like a Mollusk, but showing 

 that it is a true Articulate by its jointed legs and antennae, and its 



Figs. 160-169. 



Articulates, Figs. 160-169. — 1. Worms: 160. Arenicola marina, or Lob-worm (X%)- 2. Crus- 

 taceans : 161, Crab, species of Cancer ; 162, an Isopod, species of Porcellio ; 163, an Amphipod, 

 species of Orchestia ; 164, an Isopod, species of Serolis (XK) ! 165, 166, Sapphirina Iris; 165, 

 female, 166, male (X6); 167, Trilobite. Calymene Blumenbachii ; 168, Cy there Americana, of 

 the Cypris family (Xl2) ; 169, Anatifa, of the Cirriped tribe. 



jointed body within the shell ; 1 69, representing a Cirriped, is also 

 somewhat like a Mollusk in its shell, — though articulate in structure, 

 as the legs show, and, in fact, a Crustacean. Centipedes, and all In- 

 sects, as well as Worms, are other examples of Articulates, the body 

 consisting of a number of segments. The name of the sub-kingdom 

 is from articulus, a joint. 



V. Vertebrates. — Having (1) a jointed internal skeleton, and 

 (2) a bone-sheathed cavity along the back, for the great nervous cord, 

 distinct from the cavity for the viscera : as in Fishes, Reptiles, Birds, 

 Quadrupeds. 



The skeleton is made up of vertebrae, or the bones of the vertebral 

 column, with their appendages ; and a vertebra is the fundamental 

 element of the structure. The bone-sheathed cavity occupied by the 

 nervous cord is enclosed by processes from the upper (or dorsal) side 

 of the vertebrae, and the visceral cavity by the ribs, which are pro- 

 cesses from the lower side of the vertebrae. The legs and arms are 

 appendages to the system of vertebrae and ribs. 



Recapitulation. — In Radiates, the structure is radiate or flower- 

 like. In Mollusks, it is bag-like and simple. In Articulates, it is 

 made of a series of rings, and is composite in the structure of both 

 the skeleton and the nervous system. In Vertebrates, it contains a 

 series of vertebrae, and is composite in the skeleton ; and, besides, it 

 has separate cavities for the nervous cord and viscera. 



