64 



GENERAL ZOOLOGY 



Peripatus is of great zoological interest because it is a 

 1 ' missing link." It has many points of marked resemblance 

 to annelid worms, and at the same time possesses character- 

 istics which make it unquestionably belong to the Phylum 

 Arthropoda. The annelidan affinities are shown by: (1) 

 the paired metameric nephridia (kidneys) ; (2) the presence 

 of cilia in the reproductive organs; and (3) the general 

 arrangement of the chief systems of organs. Arthropod 

 characteristics are: (1) appendages modified as jaws; (2) 

 a body cavity mostly converted into large blood sinuses; 

 (3) the presence of tracheae for breathing; and (4) the paired 

 jointed appendages. Peripatus closely resembles the hypo- 

 thetical ancestral arthropod described at the beginning of 

 Chapter 5 (Fig. 27). 



CLASS 3. MYRIAPODA 



This class includes the centipedes and millipeds (Fig. 

 34). These animals are readily distinguished from other 



FIG. 34. At the left a centipede eating a fly; at the right millipedes resting and 



eating a leaf. 



arthropods by the following characteristics: (1) a distinct 

 head with one pair of antennae and simple eyes; (2) a long 

 body composed of many free similar segments ; (3) tracheae 

 for breathing; and (4) Malpighian tubules for excretory 

 organs. The myriapods are divided into three orders: 



Order 1. Diplopoda. These are the millipeds. As the 

 name of the order indicates, they have two pairs of jointed 



