20 INVERTEBRATE ZOOLOGY 



MYRIAPODA 



A CHILOPOD. A CENTIPED (Lithobius) 



Myriapods are worm-like animals which live under logs and 

 stones, beneath the bark of decaying stumps and trees, and 

 in other dark, damp places. The two main groups of myrio- 

 pods may be easily recognized by the differences in shape and 

 habits, the Chilopoda being flattened and very active animals 

 with one pair of legs to a segment, the Diplopoda being usually 

 cylindrical animals with short legs, two pairs of which are 

 present on most of the segments. 



Observe the vermiform body, the well-marked segmentation, 

 and the segmented legs ; also the lack of specialization among 

 the segments, there being no division into thorax and abdomen. 

 The animal is plainly an arthropod, but it is not an insect ; it 

 is a lower animal than an insect, because its body shows less 

 specialization. Note the single pair of antennae and the insect- 

 like mouth-parts, also the large hook-like appendages just back of 

 the head. These latter are homologous to the first pair of 

 legs ; they are the principal organs of prehension and are 

 provided with poison glands which open on the inner surface 

 near the end. Note the anal feelers ; these are homologous to 

 the hindermost legs and enable the animal to perceive what is 

 back of it. 



Exercise 1. Draw an outline of the dorsal aspect of the animal 

 on a scale of 5 and label all the organs observed. 



Exercise 2. Draw a ventral view of the head on a scale of 

 10, showing the cephalic appendages in position. The 

 mouth-parts consist of a pair of mandibles and two pairs 



