PRIMITIVE TRACHEATES 



399 



interest attached to Peripatus centres in the fact that it, to use 

 the words of Sedgwick, " stands absolutely alone as a kind of 

 half-way animal between the Arthropoda and Annelida ". 



Peripatus (fig. 246) is a small cylindrical animal, found among 

 rotting wood or the like, and comparable in appearance either 

 to a well-nourished caterpillar or a segmented worm. The 

 velvety skin is beautifully coloured, the tint varying according 

 to the species. The front part of the body, called 

 by courtesy the head, is not sharply marked off from 

 the trunk, and this again is not clearly segmented, 

 though its segmentation is indicated by the fact that 

 it bears numerous pairs of stumpy legs, the exact 

 number depending upon the species. These legs are 

 hollow, conical projections (much like the appen- 

 dages of some Annelids), and only exhibit in an 

 imperfect way the jointing that characterizes Arthro- 

 pods generally. Each of them is provided with a 

 couple of sharp claws at its tip. Upon the under side 

 of the head there is a swollen circular lip surrounding 

 a depression within which the mouth opens. On each 

 side of the head, outside this lip, is ,a short cylin- 

 drical projection known as oral papilla, and equiva- 

 lent to a pair of modified limbs. Upon the tip of 

 each of these is the opening of a large slime-gland, 

 which secretes a sticky substance that can be forcibly 

 ejected either as a defensive measure or else (in the 

 New Zealand species at any rate) as a means of 

 capturing prey. Within the circular lip are a pair 

 of muscular jaws, each armed with two claw-like pro- 

 jections used for chewing the food. These jaws, again, are to 

 be looked on as modified limbs, and the presence of such limb- 

 jaws is an Arthropod character, though the limitation to a single 

 pair is a peculiarity of Peripatus. A pair of cylindrical imper- 

 fectly-ringed antenncs project from the front of the head, and near 

 the base of each of them there is a simple eye. 



Only a few of the more important details regarding the in- 

 ternal structure (fig. 247) can be mentioned here, and these 

 may be conveniently grouped into: i. Arthropod characters, and 

 2. Annelid characters. 



I. Arthropod characters. — The organs of circulation con- 



Fig. 246. — Cape 



Peripatus(/'er:]^a^«s 

 Ca^ensis), enlarged 



