TAEASITES. 



commissures with the cephalic ganglion. The more distinctly 

 the articulation is marked, the more regular is the formation of 

 ganglia; the more indistinct the former, the greater is the 

 fusion of the ganglia into larger masses. 



5. A tolerably complicated motor system. In the first place, a 

 firm, hard skin, which forms hollow rings or tubes, in the interior 

 of which the muscles are attached. Here, therefore, we have 

 the organs of motion inclosed in the interior of the levers to be 

 moved, whilst in the Vertebrata the muscles are fixed on the 

 outside of the framework. And whilst in the lower animals we 

 neither meet with articulated limbs nor with levers united by 

 articulations, here we meet with limbs which consist of joints 

 united by articulations (generally ball and socket or hinge 

 joints), and serve in part for all sorts of movements upon the 

 earth (hopping, running, springing), in water (swimming), and in 

 the air (flying), in part for nutritive purposes, for the capture of 

 prey and as assistants in mastication, and partly for the perception 

 of the impressions of the senses. They allow the recognition of 

 the following individual parts : 



a. The antenna. They are sometimes double (an anterior 

 inner and posterior outer), and sometimes single on each 

 side, or apparently entirely deficient from being converted into 

 biting or raptorial organs. They stand before and over the 

 mouth upon the forehead ; lower down in embryos, and only 

 advancing upwards by degrees. They are divided into the 

 shaft (scapus), which is usually composed of several joints, and 

 the flagellum. 



b. The oral organs, which serve for piercing the prey, for 

 mastication, and closing the mouth, lie round the latter, and 

 consist originally of four pairs of lateral jaws, the first of which 

 is always, and the last generally, fused together into an oper- 

 culum-like lip. In them the following individual parts may 

 usually be distinguished : a, an upper lip (labrum) ; j3, a pair of 

 upper jaws or mandibles (mandibula) , sharp, simple, consisting of 

 a single powerful piece; -y, a pair of lower jaws or maxilla 

 (maxillae, mdchoires), which usually consist of a shaft or body 

 (stipes), a lobe, destined either for mastication or concealment, and 

 an external feeler or palpus; S, a very composite lower lip 

 (labium) . 



c. The masticating feet or foot-jaws (pates-mdchoires), which 

 form a transition between the organs of motion and nutri- 



