236 MANUAL OF ZOOLOGY SECT. 



the larval condition these are free-swimming, distinctly 

 segmented, and provided with a number of jointed append- 

 ages : in passing into the adult state they become fixed, lose 

 their segmentation though retaining some of the jointed 

 appendages, and become enclosed in a fold of the integument 

 in which are developed a series of calcareous plates. The 

 attachment of the Cirripide is by the head ; the posterior 

 portion of the body is free, and is capable of being thrust 

 out with a series of six pairs of many-jointed appendages 

 or cirri t borne on the thorax through a slit in the 

 enclosing shell. In the Barnacles the head region is drawn 

 out into a stalk (A, p.] ; in the Acorn-shells the stalk is 

 absent. 



2. THE ONYCHOPHORA 



The class Onychophora comprises only the aberrant genus 

 PeripatllS, which is interesting owing to the presence of certain 

 primitive features which afford some reason for regarding it as 

 intermediate between such forms as the Annulata on the one hand and 

 the higher Arthropoda on the other. 



Peripatus (Fig. 128) is a caterpillar-like animal of approximately 

 cylindrical form, and not divided into segments : it has a fairly well- 



FIG. 128. Peripatus capensis, lateral view. (After Balfour.) 



marked head and a series (14-42) of short stumpy appendages. The 

 integument is thrown into a number of fine transverse wrinkles, and is 

 beset with numerous conical papillae each capped with a little chitinous 

 spine. The head (Fig. 129) bears a pair of antenna, a pair of eyes, a 

 pair of jaws, and a pair of short processes the oral papillae. On the 

 surface of the oral papillae are situated a pair of glands, the slime glands. 



