ANIMAL KINGDOM. 



119 



and nervous cord in the same general cavity ; (4) having no internal 

 skeleton ; as Worms, Crustaceans, Insects. 



The articulations are made in the hardened skin, and not, as in 

 Vertebrates, in internal bones ; and the principal nervous cord passes 



152a 



Mollusks, Figs. 150-158. —1. Brachiapotts : 150. Terebratula impressa, of the Oolyte ; 151, Lin- 

 gula, on its stem. 2. Bryozoa: 152 (XS), 152 a, genus Eschara. 3. Lamellibranchs(Common 

 Bivalves) ; 153, 154; 155, the Oyster. 4. Gasleropods: 156, Helix. 5. Pteropods : 157, genus 

 Cleodora. 6. Cephalopods : 158, Nautilus (X3j?)- 



Fig. 159. 



The Calatnary or Squid, Loligo vulgaris (length of body, 6 to 12 inches) ; i the duct by which the 

 ink is thrown out; p, the " pen.'" 



heloiv the stomach and intestine, and has usually a ganglion for each 

 segment of the body, — so that the articulate structure is indicated 

 by the nervous system, as well as by the joints of the body and its 

 members. The fundamental element of the body is, hence, a segment 

 or ring containing a nervous ganglion and a portion of the viscera. 

 An Articulate is thus multiplicate in structure, or consists of suc- 

 cessive approximately similar segments or parts, and is thus unlike 

 the Mollusks. 



Some of the Articulates are shown in Figs. 160 to 169. Fig. 160 

 is a sea-shore worm; 161, a Crab ; 162 to 167, other Crustaceans; 



