HABITS AND DIGESTIVE ORGANS IN ARTICULATA. 79 



tion to their size, that, in energy and rapidity of movement, 

 some of the Articulated tribes surpass all other animals. These 

 movements are directed by organs of sensation ; which, although 

 not developed on*so high a plan as those of some Mollusca, are 

 evidently very acute in their powers. There are very few 

 instances of Articulated animals being in any way restrained as 

 to freedom of locomotion ; and these are for the most part found 

 in a single group, the CIRRHIPODA, or Barnacle tribe, which 

 connects this sub-kingdom with the preceding. In general they 

 roam freely abroad in search of food ; and they arfc supplied with 

 prehensile organs for capturing their prey, and with a complex 

 masticating apparatus for reducing it. Their actions are evi- 

 dently directed almost solely by instinctive propensities, which are 

 adapted to meet every ordinary want ; these are of similar 

 character in each individual of the same species, and present but 

 little appearance of ever being modified by Intelligence. Hence 

 these animals seem almost like machines, contrived to execute a 

 certain set of operations ; many of them, however, producing 

 immediate results, which even Man, by the highest efforts of his 

 reason, has found it difficult to attain. 



598. All the Articulata, save a few of the very lowest 

 species, possess a distinct head at one end of the body, furnished 

 with organs of special sensation, and with jaws for the prehen- 

 sion and reduction of the food. These jaws do not open vertically, 

 however, as in the Vertebrata, so as to leave a horizontal 

 aperture ; but laterally, so as to leave a vertical aperture : 

 and there are frequently several pairs of them, one behind the 

 other, sometimes furnished with sharp cutting edges, sometimes 

 having their edges toothed like a saw, and sometimes adapted to 

 crush rather than to cut or tear. The alimentary tube frequently 

 passes straight along the central line, from one extremity of the 

 body to the other, with a dilatation near its commencement, 

 the stomach : and where this is not the case, the convolutions 

 which the intestine makes are usually few in number. Instead 

 of a heart, we find a dorsal vessel (s, Figs. 290 and 291), a long 

 tube placed on the central line of the back, and divided into 

 segments, corresponding with those of the body, each seg- 



