A CENTIPED 17 



Class: Tracheata. Division: Myriapoda 

 A CENTIPED (LITHOBIUS) 



Myriapods are wormlike 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 myriapods 

 may be easily recognized by the differences in shape and habits, — 

 the centipeds (Chilopoda) being flattened and very active ani- 

 mals with one pair of legs to a segment, the millipeds (Diplopoda) 

 being usually cylindrical animals v/ith 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 ; note 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 special- 

 ization. Note the single pair of antennae and the insect-like mouth 

 parts, which consist of a pair of mandibles and two pairs of 

 maxillae ; also the large hooklike 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 poi- 

 son 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 cephaHc appendages in position. 



Exercise 3. Remove, under a dissecting microscope, the prehensile 

 hooks and the mouth parts, beginning with the posterior ones and 

 working forward, and the antennae. Mount them on a slide and 

 draw an outline of each. Compare the different structures of the 

 mouth parts with those of the insect and label them all. 



The Internal Organs. The digestive, circulatory, respiratory, 

 excretory, and nervous systems are similar to the same systems in 

 insects. They will not be studied in this dissection.. 



