286 Mr. Newport om the Class Myriapoda, Order Chilopoda, 



surface of each segment {a, b, c). These together form an elongated, trian- 

 gular surface on each side, the apex of which is directed to the median line. 

 The two pieces that form the apices of these plates, and lie nearest the median 

 line, are the two ununited sternal pieces, which represent the middle portion 

 of the segment that has almost disappeared, — the true sternum (a). Those 

 which are external to these, on each side, in like manner represent the 

 epistemal pieces (b), and those on the outside, which form the base of the 

 triangular plates, are the epimeral (c). In these parts we distinctly recognize 

 the atrophied first subsegment. But although the epimeral plates exist, not 

 even the rudiments of lateral appendages are developed, because, as I have 

 distinctly found, in every instance it is necessary that a primary structure 

 should be moulded in its general proportions before it gives origin to its 

 appendages. It is in this way, by changes that take place in the relative 

 development of the rudimentary segments of the embryo in the ovum, that 

 each animal is originally formed on a comparatively higher or lower type, 

 according to the greater or less extent of change which the embryo undergoes 

 in its earliest stages. The form impressed on the future animal, when these 

 changes in the ovum begin to be arrested, usually is that by which its further 

 development is to be regulated ; and which it may retain either as a perma- 

 nent condition, or only as a form that requires to be further matured in post- 

 embryonic life before it is fitted to take that which it is ultimately to assume. 

 It is in this way that the coalescing segments of Geophilus become further 

 united in Scolopendra, and are completely lost in single structures in Lithobitis 

 and Cermatia, in each instance the union of the rudimentary segments taking 

 place in the ovum, and the type of formation then impressed on the animal 

 being afterwards uniformly repeated at each change of tegument and produc- 

 tion of new segments. 



The mode in which development takes place, by a union of similar parts, is 

 always centripetal. When any portion of the body has acquired its fullest 

 extent by the^r*^ mode, that of simple growth or enlargement, it acquires a 

 tendency to coalesce or become united with similar adjoining structures, 

 either by simple anchylosis of the two, or by a greater or less extent of direct 

 union or coalescence, and the two parts which thus become joined tend to one 

 common centre. 



