JULID^E. 



281 



(718.) The body of a Myria/pod consists of a consecutive series of 

 segments of equal dimensions, but, unlike those of the generality of the 

 Annelida, composed of a dense semicalcareous or else of a firm cori- 

 aceous substance ; and to every segment is appended one or two pairs 

 of articulated legs, generally terminated by simple points. 



(719.) The anterior segment or head, besides the organs belonging 

 to the mouth, contains the instruments of sensation, consisting of simple 

 or compound eyes, and of two long and articulated organs called an- 

 tennae, generally regarded as appropriated to the sense of touch, but 

 which probably are connected with other perceptions less intelligible 

 to us. 



(720.) The air required for respiration is taken into the body through 

 a series of minute pores or spiracles placed on each side along the 

 entire length of the animal, and is distributed by innumerable rami- 

 fying tubes or tracheae to all parts of the system. 



(721.) The number of segments, and consequently of feet, increases 

 progressively with age, a circumstance which remarkably distinguishes 

 the Hyriapoda from the entire class of Insects, properly so called. 



(722.) The MYRIAPODA may be divided into two families, originally 

 indicated by Linnaeus : the Julidce, or millepedes, and the Scolopen- 

 dridce, or centipedes, each of which will require our notice. 



(723.) JULIDCE. The lowest division, which derives its name from 

 the Julus, or common millepede, is 

 most nearly allied to the Annelidans, 

 both in external form and also in the 

 general arrangement of its different 

 organs; this therefore we shall first 

 examine, and select the Julus ter- 

 restris, one of the species most fre- 

 quently met with, as an example of 

 the rest. These animals (fig. 139, A) 

 are generally found concealed under 

 stones, or beneath the bark of decayed 

 timber, where they find subsistence 

 by devouring decomposing animal and 

 vegetable substances. The body is 

 long and cylindrical, composed of be- 

 tween forty and fifty hard and brittle 

 rings, which, with the exception of 

 those forming the head and tail, differ 

 but slightly from each other. Every 

 segment supports two pairs of minute 

 feet, arising close to the mesial line upon the under or ventral surface ; 

 but these feet, although distinctly articulated (fig. 139, c, p), are as yet 

 extremely small in comparison with the bulk of the animal, and are 



Fig. 139. 



Julus terrestris. A, in the act of pro- 

 gression; B, the same rolled up in a spiral 

 form; C, segments of the body magnified, 

 showing the mode of attachment of the 

 feet (i, p) on each side of the mesial line 

 (r) of the abdomen. 



