i88 



SYSTEMATIC ZOOLOGY 



organs of respiration, but the group is believed to be more 

 closely related to the Arachnida than to any other. The prin- 

 cipal genus is Macrobiotus (Fig. 184). 



SUBTYPE III. TRACHEATA 



The Tracheata (Lat. trachea, air tube) in the adult condition 

 breathe exclusively by means of tubes or tracheae, which open 

 to the outside by the symmetrically placed stigmata. The 



structure of the tracheae is the same 

 as that already described for some 

 of the Arachnida. Thus these ani- 

 mals breathe air directly and are 

 essentially land or air inhabitants, 

 though some can remain under water 

 for a considerable time. The body 

 is, with one exception, distinctly 

 segmented, and the appendages are 

 never biramous, but consist of a 

 single row of segments. There is 

 always a single pair of appendages 

 anterior to the mouth ; these are the 

 antennae and are sensory in function. 

 In the Tracheata the sexes arealwavs 

 distinct. The group is divided into 

 three classes. 



FIG. 1S4. Macrobiotus kufelandi, a 

 bear animalcule; greatly enlarged. 

 bucc, buccal cavity; gld, accessory 

 gland; mctl, Malpighian tube; ov, 

 ovarv ; ret, rectum; salt, salivary 

 glands ; stom, stomach ; sty/, teeth. 

 (After Greet and Plate, from Parker 

 and Haswell's Text-book.) 



CLASS I. PROTRACHEATA 



The Protracheata ( hat.pro, before, 

 and tracheatus, provided with tra- 

 cheae), or Onychophora (Gr. ovuj-, 

 claw, and <f>opea), to bear), are repre- 

 sented by a single genus, Peripatus (Fig. 185 ), which forms to a 

 certain extent a connecting link between the Annelida and the 







Fig. 185. Peripatus caper/sis. Lateral aspect. (From Parker and Haswell's Manual.) 



