294 Mr. Newport on the Class Myriapoda, Order Chilopoda, 



ventral portion of this region, and in its enormous appendages (/to m), — the 

 articulated foot-jaws, — the analogues of the mandibles of Insects. 



This mode of tracing the formation of the head in the Chilopoda may enable 

 us to understand the principles on which the more complicated organ in the 

 higher Articulata, the hexapod Insects, is developed in the ovum : first, by an 

 aggregation of the normal constituents of the part into distinct regions ; and 

 then by the anchylosis, or the coalescence of these into one structure ; by the 

 extension backwards of the cephalic, and forwards of the basilar portions ; the 

 different configuration of the whole being dependent on the greater or less 

 extent to which individual parts are enlarged. 



Organs of Nutrition. 



To trace the analogies of these parts we must compare them with the simple 

 appendages of the segments — the legs, all the divisions of which exist, almost in 

 their relative proportions, in the mandible of the young Geophilus (fig. 3.) at that 

 stage of growth which I have elsewhere described * as the fourth period in lulus. 

 The mandible, at the bursting of the egg, is only a simple tubercle to the sixth 

 segment of the head, precisely similar in every respect, of form and size, to 

 the tubercles of other segments of the body, which afterwards become organs 

 of locomotion, &c. But during the short space of time that elapses while the 

 embryo is escaping from the egg, and before it has rid itself of the foetal mem- 

 brane, this little tubercle is enlarged to twice the size of the others, and con- 

 tinues to increase, and undergoes a change in the relative development of its 

 parts, which so modifies its whole form as to adapt it for the function of 

 prehension and manducation, instead of locomotion. The tubercles of the 

 other segments have all their parts developed equally ; but those which are 

 to become the mandibles, and be fitted for a different function, are not only 

 more rapidly enlarged, but have the coxa and femur more advanced than the 

 other articulations. In the appendages, then, as we have already seen in the 

 segments, the configuration of the whole organ, and the special adaptation 

 of its structure to a peculiar function, consist in the greater or less develop- 

 ment of its original parts, and not in the introduction of a new element into 

 its composition. The coxal articulation of the mandible (/) always exists 



* Phil. Trans., 1841, part ii. p. 121. 



