270 



METAZOAN PHYLA 



It is slightly compressed laterally, has long legs, and runs with great 

 speed. It is a beneficial form, since it preys upon various noxious insects, 

 such as cockroaches and bedbugs, which live around houses. 



308. Millipedes. — The milhpedes, or thousand-legged worms (Fig. 

 168), differ from the centipedes in several ways. The body is cylindrical 

 rather than flattened. The legs are very short, generally two pairs to 

 a segment, and the animal tends to react by rolling up into a flat 

 coil instead of by running away. There is a pair of mandibles and one 

 of maxillae, and either simple or compound eyes. The millipedes also 



Fig. 168. — A millipede, Spirobolus sp., from South Carolina. 



Natural size. 



From a preserved specimen. 



live in dark, moist places but feed principally upon plant food and 

 therefore are likely to be injurious, whereas the centipedes are likely to 

 be beneficial. 



309. Reproduction in Myriapods. — In all myriapods the sexes are 

 separate. Some millipedes are known to lay large numbers of eggs in 

 cells excavated in the ground, which are later sealed up, but in the 

 case of the centipedes the eggs are laid singly in the damp earth. The 

 larva when hatched has only a few metameres and a few legs. The larvae 

 of the millipedes have only three pairs of legs, in this respect resembling 

 insects. As the animal grows, new metameres, each with a pair of legs, 

 are added just in front of the posterior one. Thus the total number of 

 metameres in the body is an indication of the age of the individual. 



