MYRIAPODA. 



225 



they form the transition from the red-blooded worms to the class 

 of insects, and are intermediate between the two in every point of 

 their structure. 



(267.) The body of a Myriapod is composed of a consecutive 

 series of segments of equal dimensions, but, unlike those of 

 the generality of the Annelida, composed of a dense semi-calca- 

 reous, or else of a firm coriaceous substance ; and to every segment 

 is appended one or two pairs of articulated legs, generally termi- 

 nated by simple points. 



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 antenna, generally regarded as appropriated to the sense of 

 touch, but which probably are connected with other perceptions less 

 intelligible to us. 



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 

 ramifying tubes or tracheae to all parts of the system. 



The number of segments, and consequently of feet, increases 

 progressively with age ; a circumstance which remarkably distin- 

 guishes the Myriapoda from the entire class of insects, properly so 

 called. 



(268.) The Myriapoda may be divided into two families, origin- 

 ally indicated by Linnaeus : the Julidce, or millepedes ; and the Sco- 

 lopendridtf, or centipedes ; each of which will require our notice. 



Julid<. The lowest division, 

 which derives its name from the 

 Julus, or common millepede, is 

 most nearly allied to the Anneli- 

 dans, both in external form, and 

 also in the general arrangement 

 of its different organs ; this, there- 

 fore, we shall first examine, and 

 select the Julus terrestris, one 

 of the species most frequently 

 met with, as an example of the 

 rest. These animals (Jig- 98, A) 

 are generally found concealed un- 

 der stones, or beneath the bark of 

 decaying timber, where they find 



Fig. 98. 



