3 o8 



COLLEGE ZOOLOGY 



organs are air-tubes, called trachea, which open by means of 

 pores on various parts of the body. The excretory organs are 

 nephridia (14), one at the base of each leg. The vesicular end 

 of the nephridium is part of the ccelom. The nervous system 

 consists of a brain (4), dorsally situated in the head, and a pair 

 of ventral nerve-cords (6), which are connected by many trans- 

 verse nerves. The sexes are separate, and the cavities of the 

 reproductive organs are ccelomic. 



Peripatus is of special interest since its body exhibits certain 

 structures characteristic of annelids and other structures found 

 only in arthropods. It is, however, undoubtedly an arthropod. 

 The following table (XI) presents briefly these characteristics 

 and shows in what respects it differs from other arthropods : — 



TABLE XI 



THE CHARACTERISTICS OF PERTPATUS ARRANGED SO AS TO SHOW THE 

 SIMILARITY TO AND DIFFERENCES FROM ARTHROPODS AND ANNELIDS 



Arthropod 

 Characteristics 



Appendages modi- 

 fied as jaws. 



A haemocoelic body- 

 cavity. 



No coelom around 

 alimentary canal. 



Tracheae present. 



Annelid Characteristics 



Paired segmentally ar- 

 ranged nephridia. 



Cilia in reproductive 

 organs. 



Chief systems of organs 

 arranged as in anne- 

 lids. 



Structures Peculiar to 

 Peripatus 



Number and diffusion 

 of tracheal apertures. 

 Single pair of jaws. 

 Distribution of repro- 

 ductive organs. 

 Texture of skin. 

 Simplicity and simi- 

 larity of segments be- 

 hind the head. 



4. Class III. Myriapoda 



The Myriapoda (Gr. murios, ten thousand; podes, feet) are 

 terrestrial arthropods commonly known as centipedes, or wire- 

 worms. They do not constitute a compact group of animals, 

 and authorities differ with regard to their classification. The 



