AXXULOSA MYRIAPODA. 65 



3. Ametabolic (Or. a, without; melabole, change) 

 insects undergo no metamorphosis. The adult insect does 

 not differ from the young, except in point of size. These 

 insects never acquire wings. 



CLASS 2. Myriapoda. 



77. The Myriapoda (Gr.murios, ten thousand ;poda, feet) 

 is a very small class, comprising only the centipedes and 

 millipedes. These animals in many respects resemble the 

 insects, and are often included in that class. They differ 

 from the Insecta, however, in the following characters : 

 The head is distinct, but there is no marked line of 

 separation between the thorax and abdomen. There are 

 always more than twenty somites in the body. The 

 limbs are numerous, and are attached to the segments of 

 the abdomen as well as to the thorax. The eyes are 

 simple. Wings are never present. 



78. Skeleton. The myriapoda are provided with an in- 

 tegument hardened by chitine, as in the Insecta. This 

 integument is divided into somites, of which there are 

 always more than twenty. The head is always distinct, 

 but there is no marked line of division between the thorax 

 and abdomen. The head consists of five or six amal- 

 gamated somites. All the other segments of the body, 

 except the last, are exactly like one another. The limbs, 

 as the name of the class implies, are numerous, and are 

 borne by the somites that correspond to the abdomen in 

 the Insecta and Arachnida, as well as by those of the 

 thorax. Each segment bears one pair of limbs. In one 

 group, there are apparently two pairs of limbs attached to 

 each segment. It seems, however, in these cases, that 

 what appears to be a single segment, really consists of two 

 somites amalgamated together. The appendages of the 

 anterior segments are often modified into organs of 

 prehension. 



79. The internal organs of the myriapoda bear a close 

 resemblance to those of the Insecta. There is a dorsal 



15 E, E 



