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



lation, is very short and small, and gives attachment to a minute joint for 

 the claw, and also to two spines. These parts are subject to much variation 

 of form. In the Cermatiidce the metatarsus is developed to its maximum 

 extent, and the proper tarsal joints are exceedingly numerous, although the 

 primary divisions of the limbs remain the same. In the ScolopendridcG they 

 are rounded, smooth and uniform ; but in some Chilognatha, as in some spe- 

 cies of Spirostrepti , the tarsal joints are enlarged at their distal extremity, 

 and the under surface of one or more of them is often developed into a soft 

 cushion or pad, as in many insects. 



Of the Development of the Segments. 



I have already stated that the two arches of the segments are developed 

 more uniformly in the Chilopoda than in any other Articulata. Although I 

 regard this order of Myriapoda as higher in general development than the 

 Chilognatha, yet the latter have the dorsal surface of the body developed to a 

 much greater, and the ventral to a much less extent. In the Chilopoda we 

 have seen that the ventral region of the body, in which the principal animal 

 structures are situated, is broad and powerful, and indicatory of the great 

 strength and activity of the individual. In the Chilognatha, on the contrary, 

 the ventral surface is almost completely atrophied or greatly retarded in its 

 development ; while the dorsal surface — the region in which the circulatory 

 and secretory organs, that minister chiefly to the vegetative functions of life, 

 are placed, — is developed to its maximum extent. 



We are already aware that it is by a gradual approximation and union of 

 two or more segments, that have acquired their full growth, that the body is 

 divided into separate regions in hexapod Insects. In like manner it is on the 

 union of two segments, or the gradual disappearance of one, and its coalescence 

 with another, that the different but more rudimentary forms of body in the 

 Myriapoda entirely depend. In the Chilognatha the normal segments pro- 

 duced at each change of tegument remain perfectly distinct throughout life, 

 and only acquire their full size by that increment which I have elsewhere de- 

 scribed* as the first mode of development, — simple growth. But even in the 

 lowest forms of Chilognatha, in which this first mode is chiefly predominant, 

 * Philosophical Transactions, 1843, part 2. p. 244. 



