56 INTRODUCTION TO CLASSIFICATION. 



ever, help out our diagnosis in practice. They never possess 

 more than four pairs of locomotive limbs, and the somites of 

 the abdomen, even when the latter is well developed, are not 

 provided with limbs. Again, in the higher Arachnida (Fig. 28), 

 as in the higher Crustacea, the body is composed of twenty 

 somites, six of which are allotted to the head ; but, in the 

 former class, one of the two normal pairs of antennae is never 

 developed, and the eyes are always sessile, while, in the highest 

 Crustacea, the eyes are mounted upon moveable peduncles, and 

 both pairs of antennae are developed. 



XXII. THE MYKIAPODA. 



The Centipedes and Millipedes (Fig. 29) have the chitinous 

 integument of the body divided into somites, provided with 



Fig. 29. 



Fig. 29. Anterior part of the body of Scolopendra Hopei (after Newport). A, Anterior 

 part of the body from above; B, from below ; A, head proper; 15, anterior thoracic 

 somites; a, antennae; C, antennae, labrum, and mandibles (iv') from below ; D, under 

 view of head, with the two pairs of maxilla (v' vi') covering the foregoing. 



articulated appendages; and nervous and circulatory organs 

 constructed upon a similar plan to those of the former groups. 



